Tid1 Isoforms Are Mitochondrial DnaJ-like Chaperones with Unique Carboxyl Termini That Determine Cytosolic Fate

Abstract

Tid1 is a human homolog of bacterial DnaJ and the Drosophila tumor suppressor Tid56 that has two alternatively spliced isoforms, Tid1-long and -short (Tid1-L and -S), which differ only at their carboxyl termini. Although Tid1 proteins localize overwhelmingly to mitochondria, published data demonstrate principally nonmitochondrial protein interactions and activities. This study was undertaken to determine whether Tid1 proteins function as mitochondrial DnaJ-like chaperones and to resolve the paradox of how proteins targeted primarily to mitochondria function in nonmitochondrial pathways. Here we demonstrate that Tid1 isoforms exhibit a conserved mitochondrial DnaJ-like function substituting for the yeast mitochondrial DnaJ-like protein Mdj1p. Like Mdj1p, Tid1 localizes to human mitochondrial nucleoids, which are large protein complexes bound to mitochondrial DNA. Unlike other DnaJs, Tid1-L and -S form heterocomplexes; both unassembled and complexed Tid1 are observed in human cells. Results demonstrate that Tid1-L has a longer residency time in the cytosol prior to mitochondrial import as compared with Tid1-S; Tid1-L is also significantly more stable in the cytosol than Tid1-S, which is rapidly degraded. The longer cytosolic residency time and the half-life of Tid1-L are explained by its interaction with cytosolic Hsc70 and potential protein substrates such as the STAT1 and STAT3 transcription factors. We show that the unique carboxyl terminus of Tid1-L is required for interaction with Hsc70 and STAT1 and -3. We propose that the association of Tid1 with chaperones and/or protein substrates in the cytosol provides a mechanism for the alternate fates and functions of Tid1 in mitochondrial and nonmitochondrial pathways. Tid1 is a human homolog of bacterial DnaJ and the Drosophila tumor suppressor Tid56 that has two alternatively spliced isoforms, Tid1-long and -short (Tid1-L and -S), which differ only at their carboxyl termini. Although Tid1 proteins localize overwhelmingly to mitochondria, published data demonstrate principally nonmitochondrial protein interactions and activities. This study was undertaken to determine whether Tid1 proteins function as mitochondrial DnaJ-like chaperones and to resolve the paradox of how proteins targeted primarily to mitochondria function in nonmitochondrial pathways. Here we demonstrate that Tid1 isoforms exhibit a conserved mitochondrial DnaJ-like function substituting for the yeast mitochondrial DnaJ-like protein Mdj1p. Like Mdj1p, Tid1 localizes to human mitochondrial nucleoids, which are large protein complexes bound to mitochondrial DNA. Unlike other DnaJs, Tid1-L and -S form heterocomplexes; both unassembled and complexed Tid1 are observed in human cells. Results demonstrate that Tid1-L has a longer residency time in the cytosol prior to mitochondrial import as compared with Tid1-S; Tid1-L is also significantly more stable in the cytosol than Tid1-S, which is rapidly degraded. The longer cytosolic residency time and the half-life of Tid1-L are explained by its interaction with cytosolic Hsc70 and potential protein substrates such as the STAT1 and STAT3 transcription factors. We show that the unique carboxyl terminus of Tid1-L is required for interaction with Hsc70 and STAT1 and -3. We propose that the association of Tid1 with chaperones and/or protein substrates in the cytosol provides a mechanism for the alternate fates and functions of Tid1 in mitochondrial and nonmitochondrial pathways. Tid1 is a human homolog of bacterial DnaJ and the Tid56 tumor suppressor of Drosophila melanogaster. DnaJ-like proteins function as co-chaperones with DnaK-like ATPases to promote the folding, translocation, and/or degradation of polypeptides (1Bukau B. Horwich A. Cell. 1998; 92: 351-366Abstract Full Text Full Text PDF PubMed Scopus (2435) Google Scholar, 2Gething M.J. Gething M.J. Guide Book Series. Oxford University Press, New York1997: 89-130Google Scholar, 3Voos W. Rottgers K. Biochim. Biophys. Acta. 2002; 1592: 51-62Crossref PubMed Scopus (251) Google Scholar). DnaJ- and DnaK-like proteins are highly conserved, and homologs are found in nearly every compartment of the eukaryotic cell and in several tumor viruses (4Kelley W.L. Georgopoulos C. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 3679-3684Crossref PubMed Scopus (138) Google Scholar). In Drosophila, the absence of Tid56 results in abnormal differentiation and morphogenesis, giving rise to Tumorous imaginal discs that lead to lethality during early development (5Kurzik-Dumke U. Gundacker D. Renthrop M. Gateff E. Dev. Genet. 1995; 16: 64-76Crossref PubMed Scopus (65) Google Scholar). The mechanism underlying Tid56 function is unknown. In humans, two alternatively spliced forms of Tid1 are expressed, Tid1-long (Tid1-L) and Tid1-short (Tid1-S), that differ only at their carboxyl-terminal tails (Fig. 1A) (6Syken J. De-Medina T. Münger K. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 8499-8504Crossref PubMed Scopus (125) Google Scholar). Tid1-L contains 33 amino acids unique to its carboxyl terminus, whereas Tid1-S has 6 amino acids (Fig. 1A). Both Tid1-L and -S have a predicted amino-terminal mitochondrial targeting sequence as well as the signature J-domain carrying an HPD motif required for stimulating the ATPase activity of eukaryotic DnaK-like chaperones (1Bukau B. Horwich A. Cell. 1998; 92: 351-366Abstract Full Text Full Text PDF PubMed Scopus (2435) Google Scholar, 2Gething M.J. Gething M.J. Guide Book Series. Oxford University Press, New York1997: 89-130Google Scholar, 3Voos W. Rottgers K. Biochim. Biophys. Acta. 2002; 1592: 51-62Crossref PubMed Scopus (251) Google Scholar). Experiments in mice show that Tid1 is critical for early mammalian development (7Lo J.F. Hayashi M. Woo-Kim S. Tian B. Huang J.F. Fearns C. Takayama S. Zapata J.M. Yang Y. Lee J.D. Mol. Cell. Biol. 2004; 24: 2226-2236Crossref PubMed Scopus (43) Google Scholar). Mice specifically deficient in Tid1 in the heart develop dilated cardiomyopathy, progressive respiratory chain deficiency, and decreased copy number of mtDNA (8Hayashi M. Imanaka-Yoshida K. Yoshida T. Wood M. Fearns C. Tatake R.J. Lee J.D. Nat. Med. 2006; 12: 128-132Crossref PubMed Scopus (67) Google Scholar). The vast majority of Tid1 localizes to mitochondria (6Syken J. De-Medina T. Münger K. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 8499-8504Crossref PubMed Scopus (125) Google Scholar, 9Kurzik-Dumke U. Debes A. Kaymer M. Dienes P. Cell Stress Chaperones. 1998; 3: 12-27Crossref PubMed Scopus (20) Google Scholar); however, its reported protein interactions and functions are primarily nonmitochondrial (10Sarkar S. Pollack B.P. Lin K.-T. Kotenko S.V. Cook J.F. Lewis A. Petska S. J. Biol. Chem. 2001; 276: 49034-49042Abstract Full Text Full Text PDF PubMed Scopus (51) Google Scholar, 11Cheng H. Cenciarelli C. Tao M. Parks W.P. Cheng-Mayer C. J. Biol. Chem. 2002; 277: 20605-20610Abstract Full Text Full Text PDF PubMed Scopus (39) Google Scholar, 12Cheng H. Cenciarelli C. Shao Z. Vidal M. Parks W.P. Pagano M. Cheng-Mayer C. Curr. Biol. 2001; 11: 1771-1775Abstract Full Text Full Text PDF PubMed Scopus (67) Google Scholar, 13Eom C.Y. Lehman I.R. Proc. Natl. Acad. Sci. U. S. A. 2002; 99: 1894-1898Crossref PubMed Scopus (34) Google Scholar, 14Liu H.Y. MacDonald J.I. Hryciw T. Li C. Meakin S.O. J. Biol. Chem. 2005; 280: 19461-19471Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar, 15Kim S.W. Chao T.H. Xiang R. Lo J.F. Campbell M.J. Fearns C. Lee J.D. Cancer Res. 2004; 64: 7732-7739Crossref PubMed Scopus (47) Google Scholar, 16Kim S.W. Hayashi M. Lo J.F. Fearns C. Xiang R. Lazennec G. Yang Y. Lee J.D. Cancer Res. 2005; 65: 8784-8791Crossref PubMed Scopus (39) Google Scholar, 18Tarunina M. Alger L. Chu G. Munger K. Gudkov A. Jat P.S. Mol. Cell. Biol. 2004; 24: 10792-10801Crossref PubMed Scopus (24) Google Scholar, 19Torregroza I. Evans T. Biochem. J. 2006; 393: 311-320Crossref PubMed Scopus (7) Google Scholar, 20Trentin G.A. He Y. Wu D.C. Tang D. Rozakis-Adcock M. FEBS Lett. 2004; 578: 323-330Crossref PubMed Scopus (22) Google Scholar). Tid1 has been shown to interact directly with cytosolic and nuclear proteins, which include the following: E7, an oncoprotein of human papillomavirus (21Schilling B. De-Medina T. Syken J. Vidal M. Münger K. Virology. 1998; 247: 74-85Crossref PubMed Scopus (90) Google Scholar); Tax, a transcriptional activator from human T-cell leukemia virus type 1 (11Cheng H. Cenciarelli C. Tao M. Parks W.P. Cheng-Mayer C. J. Biol. Chem. 2002; 277: 20605-20610Abstract Full Text Full Text PDF PubMed Scopus (39) Google Scholar, 12Cheng H. Cenciarelli C. Shao Z. Vidal M. Parks W.P. Pagano M. Cheng-Mayer C. Curr. Biol. 2001; 11: 1771-1775Abstract Full Text Full Text PDF PubMed Scopus (67) Google Scholar); UL9, an origin binding protein from herpes simplex virus type 1 (13Eom C.Y. Lehman I.R. Proc. Natl. Acad. Sci. U. S. A. 2002; 99: 1894-1898Crossref PubMed Scopus (34) Google Scholar); the protein G.A. S. S. J. Lin Y. Rozakis-Adcock M. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar); a (10Sarkar S. Pollack B.P. Lin K.-T. Kotenko S.V. Cook J.F. Lewis A. Petska S. J. Biol. Chem. 2001; 276: 49034-49042Abstract Full Text Full Text PDF PubMed Scopus (51) Google Scholar); H.Y. MacDonald J.I. Hryciw T. Li C. Meakin S.O. J. Biol. Chem. 2005; 280: 19461-19471Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar); and a protein in S. T. H. M. T. H. 2002; PubMed Scopus Google Scholar). The functions of Tid1 include of cell and in to in that are for by and several that Tid1 proteins function as mitochondrial DnaJ-like Tid1-L and -S and interact with potential determine whether Tid1 functions In study we demonstrate that Tid1 proteins exhibit a conserved mitochondrial DnaJ-like substituting for the yeast mitochondrial DnaJ-like protein in a Like Mdj1p, Tid1-L and -S localize to human mitochondrial nucleoids, which are large protein complexes with show that other DnaJ-like proteins Tid1-L and -S are only in an unassembled also as that Tid1-L has a significantly longer residency time in the cytosol prior to mitochondrial in to with of Tid1-L and -S their amino-terminal mitochondrial targeting and exhibit fates in the is whereas is rapidly degraded. that the cytosolic residency time and of Tid1-L explained by interactions Results from show that unassembled Tid1-L with cytosolic whereas Tid1-S Tid1-L also with the cytosolic STAT1 and We show that the unique carboxyl terminus of Tid1-L is for interactions with Hsc70 and the potential substrates STAT1 and results the that the and function of Tid1 proteins both and of mitochondria are by cytosolic protein specifically the unique carboxyl of Tid1-L -S in and and both Tid1 isoforms, to as and Hsc70 the and STAT1 and also in mitochondrial transcription by of In and by in mammalian Tid1 for in Tid1 the mitochondrial targeting sequence predicted by acids by yeast carrying the that a of B. B. J.M. W. E. Mol. Cell. Biol. 16: PubMed Scopus Google was with for the of type of the was by to in the to the cell yeast the and and the yeast at the and by of Cell in with and at to of STAT1 with for with for at from as L. E. J. Mol. Biol. Cell. PubMed Scopus Google Scholar). mitochondria in and with an of to a of of mitochondrial was to a of and mitochondria by to a of for the was at for in a and was in as and of of of of of and of in 1 1 1 and at for The and for of mtDNA and mtDNA from with of with for and a at for to and in and have been B. T. Lee I. PubMed Scopus Google Scholar). protein was in and was the cell with at protein was for at and with as In the cell mitochondrial with the unique carboxyl terminus of Tid1-S to determine whether the other was In the the was with to determine whether unassembled isoforms was by in for prior to with for the time as in protein was and by was as B. T. Lee I. PubMed Scopus Google Scholar). to with and with with at by with was Tid1-L and -S DnaJ-like function of mitochondrial DnaJ-like chaperones is in the yeast mitochondrial DnaJ-like protein is for the of proteins and for the of that Mdj1p, mitochondrial also to as and the mitochondrial protein and the degradation of is also in large mitochondrial nucleoids, and is for the mtDNA in an during cell A. K. J. J. Biol. Chem. 2002; 277: Full Text Full Text PDF PubMed Scopus Google Scholar, M. A. B. W. E. J. Mol. Cell. Biol. 1999; PubMed Scopus Google Scholar). are for mitochondrial DnaJ-like in mammalian we whether Tid1 proteins for in Tid1-L and -S in a that a of Mdj1p. type and at to the and that mitochondrial of Tid1-L -S the of at (Fig. Tid1 proteins in the and degradation of mitochondrial of the amino-terminal mitochondrial targeting sequence of Tid1 from amino acids 1 to as predicted by activity (Fig. Tid1 import the mitochondrial was required for of the mammalian mitochondrial targeting are in however, the amino-terminal sequence of Tid1 was to import yeast of DnaJ-like proteins demonstrate that the HPD motif the J-domain is for stimulating the ATPase activity of a DnaK-like protein J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). J-domain of Tid1 in which the conserved at was by a in and to the at (Fig. that Tid1-L and -S with of the unique carboxyl terminus of Tid1-L with of the (Fig. that the unique carboxyl terminus of Tid1 proteins was for The of the J-domain to for was to a of protein Tid1 proteins in at with the of which was at for that we (Fig. has shown that is with the mitochondrial B. B. J.M. W. E. Mol. Cell. Biol. 16: PubMed Scopus Google Scholar, C. B. C. E. B. W. Cell. Full Text PDF PubMed Scopus Google and bound to mtDNA A. K. J. J. Biol. Chem. 2002; 277: Full Text Full Text PDF PubMed Scopus Google Scholar). Experiments to determine the of Tid1 in human cells. the of and L. E. J. Mol. Biol. Cell. PubMed Scopus Google Scholar). In mitochondrial from more Tid1-S than Tid1-L was a of Tid1-S to Tid1-L was in cell and determine the of mitochondria with and the Tid1 to the and was in the (Fig. In a the mitochondrial to the and was in the The and to in and results that the and the mitochondrial to the (Fig. and which mtDNA The and for a time with and to a which was required to proteins such as from the and the Tid1-L and -S with the in the and (Fig. and found with the in the (Fig. Tid1 proteins are to the and with mitochondrial results demonstrate that Tid1-L and -S exhibit a conserved activity in yeast and as mitochondrial DnaJ-like proteins in human which with mitochondrial as as Tid1-L and -S in the of Tid1-L and determine the of complexed and unassembled cell with the unique carboxyl terminus of Tid1-S to determine whether the was the was to a the unique carboxyl terminus of Tid1-L to determine whether unassembled Tid1-L was the complexed and unassembled Tid1-S also by that was in the and in the (Fig. The of was as shown in In cell as well as in mitochondrial from Tid1-L and -S found to with in the (Fig. and and that the of and isoforms in Tid1 was in cell and mitochondrial (Fig. and and that unassembled Tid1-L and -S also in both cell and mitochondrial (Fig. and and In the of Tid1-S was than Tid1-L in both cell and in mitochondria (Fig. and We observed that the of Tid1-L and -S the cell in the of Tid1-L and -S is (Fig. cell that Tid1-L and -S also found in both a as well as in an unassembled (Fig. In that the of and isoforms in Tid1 in cell was and (Fig. and Tid1-L a to and as with and of Tid1-L and -S by and that as well as Tid1 to mitochondria (Fig. and In Tid1-L and -S with the mitochondrial (Fig. in Tid1-L and -S with (Fig. and that Tid1-L and -S as proteins that to the mitochondrial form (Fig. Tid1-L -S with for and for to of Tid1 that the of Tid1-S was in the of Tid1-S was to the mitochondrial the of Tid1-L was more in the of the Tid1-L was as the and a the protein was mitochondria, both Tid1-L and -S for the The cytosolic of Tid1-L and -S was by the half-life of cytosolic Tid1 and their mitochondrial targeting that and with (Fig. and proteins the cytosol with cytosolic protein that was rapidly a and a was observed (Fig. a significantly longer a was (Fig. The unique carboxyl terminus of Tid1-L data the that Tid1-L interact with cytosolic proteins in by degradation the The interaction of Tid1-L with cytosolic proteins also the mitochondrial import of Tid1-L as compared with Tid1-S as shown in Hsc70 with and DnaJ-like proteins have been shown to interact with DnaK-like proteins, which function as a in the folding, translocation, and degradation of polypeptides (1Bukau B. Horwich A. Cell. 1998; 92: 351-366Abstract Full Text Full Text PDF PubMed Scopus (2435) Google Scholar, Curr. Biol. 2001; 11: Full Text Full Text PDF PubMed Scopus Google Scholar, J.M. Mol. Biol. 2002; PubMed Scopus Google Scholar, P. D. D. T. 2004; PubMed Scopus Google Scholar). The of Tid1-L and -S to for yeast in a that Tid1 with In has been shown that mitochondrial proteins in the cytosol interact with cytosolic which the mitochondrial import W. Mol. Cell. 11: Full Text Full Text PDF PubMed Scopus Google Scholar, Cell. Full Text Full Text PDF PubMed Scopus Google Scholar, T. T. M. S. K. M. T. J. Biol. Chem. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar). to determine the to which Tid1-L and -S interact with and Tid1-L and -S from cell with and was to Tid1 of as by Tid1-L a of cytosolic Hsc70 as compared with Tid1-S (Fig. Tid1 isoforms also (Fig. with results shown in and E. determine more whether Tid1-L -S bound to in cell with that Hsc70 was (Fig. with that unassembled Tid1-L was with Hsc70 (Fig. in the Hsc70 was (Fig. with that unassembled Tid1-S with Hsc70 (Fig. results that Hsc70 was with unassembled Tid1-L and that significantly Hsc70 with unassembled Tid1-S with Tid1 of results from that Tid1-L of the which is an mitochondria that mitochondrial Tid1-L -S interact with Hsc70 the that Tid1-L with Hsc70 in the Tid1 isoforms differ only at their carboxyl that association with The mitochondrial targeting sequence of Tid1 is potential of interaction with mitochondrial the amino acids and for mammalian cell (Fig. and in at to type Tid1 with the observed in yeast (Fig. of to amino acids the carboxyl terminus of Tid1-L and the of by of the unique carboxyl-terminal Hsc70 required the of that Tid1 as well as the of complexes in of the of the a of carboxyl-terminal in which the amino-terminal targeting sequence was by the of the to the Tid1 from of Tid1 proteins that Hsc70 only with Hsc70 was with results are with data that of Hsc70 with unassembled Tid1-L as compared with unassembled results also show that the mitochondrial targeting sequence of Tid1 was for Hsc70 of more amino acids from the carboxyl terminus of with Hsc70 results that the unique carboxyl terminus of Tid1-L contains a sequence that Hsc70 association the of Tid1-L that Hsc70 STAT1 and STAT3 with and Hsc70 with to form a cytosolic in the and function of protein in the function of such a the of protein has shown that Tid1-L -S to the of transcription (10Sarkar S. Pollack B.P. Lin K.-T. Kotenko S.V. Cook J.F. Lewis A. Petska S. J. Biol. Chem. 2001; 276: 49034-49042Abstract Full Text Full Text PDF PubMed Scopus (51) Google Scholar). of Tid1-L -S in of a is by sequence from that study also that Tid1 proteins with as well as with the we whether Tid1-L -S interact with of the The interaction Tid1 and STAT1 and was in as their of Tid1-L STAT1 as well as by Tid1-S interaction with (Fig. with Tid1-L with STAT1 (Fig. The of STAT1 observed in the was by Tid1-L in with for was by which that unassembled Tid1-L with STAT1 and whereas unassembled Tid1-S (Fig. STAT3 in was Tid1-L STAT3 in the and absence of whereas Tid1-S (Fig. We to the association of Tid1-L with the two by in cell Results of that unassembled Tid1-L with whereas Tid1-S with of STAT3 (Fig. determine whether the carboxyl terminus of Tid1-L was required for the Results that of more amino acids from the carboxyl-terminal of with STAT1 and interactions (Fig. results demonstrate that the unique carboxyl-terminal of Tid1-L is for interactions only with Hsc70 also with the potential cytosolic protein substrates STAT1 and The of Tid1 proteins in a of the and has been (7Lo J.F. Hayashi M. Woo-Kim S. Tian B. Huang J.F. Fearns C. Takayama S. Zapata J.M. Yang Y. Lee J.D. Mol. Cell. Biol. 2004; 24: 2226-2236Crossref PubMed Scopus (43) Google Scholar, M. Imanaka-Yoshida K. Yoshida T. Wood M. Fearns C. Tatake R.J. Lee J.D. Nat. Med. 2006; 12: 128-132Crossref PubMed Scopus (67) Google Scholar, 14Liu H.Y. MacDonald J.I. Hryciw T. Li C. Meakin S.O. J. Biol. Chem. 2005; 280: 19461-19471Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar, 15Kim S.W. Chao T.H. Xiang R. Lo J.F. Campbell M.J. Fearns C. Lee J.D. Cancer Res. 2004; 64: 7732-7739Crossref PubMed Scopus (47) Google Scholar, 16Kim S.W. Hayashi M. Lo J.F. Fearns C. Xiang R. Lazennec G. Yang Y. Lee J.D. Cancer Res. 2005; 65: 8784-8791Crossref PubMed Scopus (39) Google Scholar, E. E. S. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar, 18Tarunina M. Alger L. Chu G. Munger K. Gudkov A. Jat P.S. Mol. Cell. Biol. 2004; 24: 10792-10801Crossref PubMed Scopus (24) Google Scholar, 19Torregroza I. Evans T. Biochem. J. 2006; 393: 311-320Crossref PubMed Scopus (7) Google Scholar, 20Trentin G.A. He Y. Wu D.C. Tang D. Rozakis-Adcock M. FEBS Lett. 2004; 578: 323-330Crossref PubMed Scopus (22) Google Scholar, Münger K. 2004; PubMed Scopus (26) Google Scholar, J.F. H. Fearns C. Yang Y. Lee J.D. J. 2005; PubMed Scopus Google Scholar). the mechanism underlying Tid1 function mitochondria is Results demonstrate that Tid1-L and -S exhibit a conserved DnaJ-like activity the mitochondrial is to the yeast mitochondrial DnaJ-like protein (Fig. The of Tid1 proteins to for an J-domain that is required for stimulating the ATPase activity of and an amino-terminal mitochondrial targeting results that Tid1 with and functions as a in yeast and mammalian Like Mdj1p, Tid1-L and -S with mitochondrial from human cells. show that is required for the of mtDNA and is in mtDNA in an during cell A. K. J. J. Biol. Chem. 2002; 277: Full Text Full Text PDF PubMed Scopus Google Scholar, M. A. B. W. E. J. Mol. Cell. Biol. 1999; PubMed Scopus Google Scholar). data the conserved function of Tid1 in the and degradation of mitochondrial proteins as well as in the of Unlike other DnaJ-like proteins, Tid1-L and -S are as both and unassembled proteins in mitochondria and cell (Fig. and and and show that the eukaryotic DnaJ-like proteins and function as J. B. 11: Full Text Full Text PDF PubMed Scopus Google Scholar, B. Lee S. Full Text Full Text PDF PubMed Scopus Google Scholar). is that Tid1 isoforms function as both and are required to determine the of Tid1 complexes and the to which and in mitochondria other The of the two isoforms in mitochondria and cell the cell type in is more Tid1-S than whereas in the of Tid1 isoforms is the (Fig. that the and of Tid1 isoforms a for and the function of Tid1-L and -S have significantly of protein import mitochondria and residency in the cytosol (Fig. show that the cytosolic of Tid1-S is during a the majority of Tid1-S was to the mitochondrial the of Tid1-L was during the Tid1-L was the form observed and was a two to as Tid1-L and -S have of protein import mitochondria as by and Tid1-L and -S have to in the The cytosolic of Tid1-L and -S was by the of Tid1 their mitochondrial targeting and Results show that is more to protein a protein is is significantly more of the protein is that and are both nonmitochondrial and the also to to the and to the however, from its and cytosolic protein as compared with The to protein degradation and of mitochondrial protein import of Tid1-L and -S with in their association with Hsc70 and cytosolic protein substrates and Tid1-L with Hsc70 and proteins such as STAT1 and its cytosolic and of mitochondrial Tid1-S with Hsc70 STAT1 in the absence of such protein interactions Tid1-S is and is in the Results of show that primarily unassembled Tid1-L with the Hsc70 and STAT1 and -3. Tid1-L is complexed with Tid1-S, association with Hsc70 is (Fig. and interaction unassembled Tid1-L and Hsc70 is in of the interaction DnaJ- and DnaK-like proteins (1Bukau B. Horwich A. Cell. 1998; 92: 351-366Abstract Full Text Full Text PDF PubMed Scopus (2435) Google Scholar, C.Y. Lee S. Cell Stress Chaperones. PubMed Scopus Google Scholar). In unassembled Tid1-L the transcription STAT1 and by unassembled Tid1-S with (Fig. demonstrate that STAT1 and STAT3 are in the cytosol as STAT1 and are and the to the promote Sci. Scholar, M. Cell. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar, Nat. Mol. Cell Biol. 2002; 3: PubMed Scopus Google Scholar, 2002; PubMed Scopus Google Scholar, Cell. 12: PubMed Scopus Google Scholar, 1997; 277: PubMed Scopus Google Scholar). results show that of Tid1-L of Tid1-L results in an of transcription and an in STAT1 S. and C. K. are required to determine whether Tid1-L and Hsc70 function as a that STAT1 and other nonmitochondrial The is to resolve the paradox of how proteins targeted primarily to mitochondrial function in nonmitochondrial (Fig. Tid1 that is in the cytosol as a protein has alternate Like other mitochondrial proteins by nuclear and in the Tid1 an amino-terminal targeting sequence that its the mitochondrial (Fig. import the targeting is the mitochondrial which functions in mitochondrial and Tid1 also has an alternate in the In study we show that Tid1-L is at with the cytosolic proteins Hsc70 and STAT1 and and potential for the nonmitochondrial of Tid1 are shown (Fig. and In Tid1 proteins with cytosolic Hsc70 and/or proteins, which protein import and (Fig. in the nonmitochondrial of Tid1 the of Tid1 the and of the mitochondria, by of the targeting sequence and of the protein the cytosol (Fig. has been shown to in to the cytosol as well as the and C. E. W. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google that is the mitochondrial and its targeting sequence is C. E. W. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). The majority of the and the is the In the results Hsc70 was shown to only with Tid1-L that is and the form We to whether STAT1 STAT3 the form of however, STAT1 for in cells. we the association of Tid1-L with the which STAT1 and has shown that Tid1 and interact with directly in the yeast and in mammalian (10Sarkar S. Pollack B.P. Lin K.-T. Kotenko S.V. Cook J.F. Lewis A. Petska S. J. Biol. Chem. 2001; 276: 49034-49042Abstract Full Text Full Text PDF PubMed Scopus (51) Google Scholar). in was found to both the and form of in the absence of only the form of Tid1-L results that Tid1-L also with nonmitochondrial proteins such as STAT3 in the The and of Tid1-L and -S cell of in the of Tid1 and as well as in the of the of cytosolic and is Tid1 more in the In is that in cell the unique carboxyl terminus of Tid1-S, also interactions with a of chaperones and protein substrates in the its cytosolic and interactions are predicted to required for the nonmitochondrial and function of are required to determine the underlying the alternate fates and functions of Tid1 and whether cytosolic of Tid1 mitochondrial We are to D. and K. for critical of with