Up-regulation of Skp2 after Prostate Cancer Cell Adhesion to Basement Membranes Results in BRCA2 Degradation and Cell Proliferation

Abstract

Aberrant interaction of carcinoma cells with basement membranes (BM) is a fundamental pathophysiological process that initiates a series of events resulting in cancer cell invasion and metastasis. In this report, we describe the results of our investigations pertaining to the events triggered by the adhesion of normal (PNT1A) and highly metastatic (PC-3) prostate cells onto BM proteins. Unlike PNT1A, PC-3 cells adhered avidly to Matrigel BM matrix as well as to isolated collagen type IV, laminin, and heparan sulfate proteoglycan perlecan, main BM components. This aberrantly increased cancer cell adhesion resulted in sustained BRCA2 protein depletion and vigorous cell proliferation, a cascade triggered by β1 integrin-mediated phosphatidylinositol 3-kinase activation leading to BRCA2 degradation in the proteasome. This latter effect was orchestrated by phosphatidylinositol 3-kinase-dependent up-regulation of Skp2, a subunit of the Skp1-Cul1-F-box protein ubiquitin complex that directly associates with BRCA2 as demonstrated by coimmunoprecipitation assays, determines its ubiquitination, and ultimately targets it for proteasomal degradation. Inhibition of Skp2 expression by small interference RNA prevented BRCA2 depletion and inhibited the trophic effect upon cell proliferation. These results provide additional evidence on the role of BRCA2 as a modulator of cancer cell growth and elucidate the molecular mechanisms involved in its down-regulation in cancer cells when interacting with BM, a crucial step in the biology of metastasis. Furthering the understanding of this molecular pathway may prove valuable in designing new therapeutic strategies aimed at modifying the natural history of prostate carcinoma. Aberrant interaction of carcinoma cells with basement membranes (BM) is a fundamental pathophysiological process that initiates a series of events resulting in cancer cell invasion and metastasis. In this report, we describe the results of our investigations pertaining to the events triggered by the adhesion of normal (PNT1A) and highly metastatic (PC-3) prostate cells onto BM proteins. Unlike PNT1A, PC-3 cells adhered avidly to Matrigel BM matrix as well as to isolated collagen type IV, laminin, and heparan sulfate proteoglycan perlecan, main BM components. This aberrantly increased cancer cell adhesion resulted in sustained BRCA2 protein depletion and vigorous cell proliferation, a cascade triggered by β1 integrin-mediated phosphatidylinositol 3-kinase activation leading to BRCA2 degradation in the proteasome. This latter effect was orchestrated by phosphatidylinositol 3-kinase-dependent up-regulation of Skp2, a subunit of the Skp1-Cul1-F-box protein ubiquitin complex that directly associates with BRCA2 as demonstrated by coimmunoprecipitation assays, determines its ubiquitination, and ultimately targets it for proteasomal degradation. Inhibition of Skp2 expression by small interference RNA prevented BRCA2 depletion and inhibited the trophic effect upon cell proliferation. These results provide additional evidence on the role of BRCA2 as a modulator of cancer cell growth and elucidate the molecular mechanisms involved in its down-regulation in cancer cells when interacting with BM, a crucial step in the biology of metastasis. Furthering the understanding of this molecular pathway may prove valuable in designing new therapeutic strategies aimed at modifying the natural history of prostate carcinoma. Up-regulation of Skp2 after prostate cancer cell adhesion to basement membranes results in BRCA2 degradation and cell proliferation.Journal of Biological ChemistryVol. 289Issue 25PreviewVOLUME 281 (2006) PAGES 22100–22107 Full-Text PDF Open Access Basement membranes (BM) 2The abbreviations used are: BM, basement membranes; ECM, extracellular matrix; COL4, collagen type IV; LN, laminin; FN, fibronectin; PLN, perlecan; MAPK, mitogen-activated protein kinase; ERK, extracellular signal-regulated kinase; PI 3-kinase, phosphatidylinositol 3-kinase; Me2SO, dimethyl sulfoxide; E3, ubiquitin-protein isopeptide ligase; siRNA, small interference RNA. are thin layers of specialized extracellular matrix (ECM) that surround and closely associate with epithelial and endothelial cells, muscle fibers, and nerves. They consist mostly of collagen type IV (COL4) admixed with laminins (LN), nidogens, and the heparan sulfate proteoglycan perlecan (PLN) and may contain small amounts of fibronectin (FN) (1Kalluri R. Nat. Rev. Cancer. 2003; 3: 422-433Crossref PubMed Scopus (1335) Google Scholar, 2Erickson A.C. Couchman J.R. J. Histochem. Cytochem. 2000; 48: 1291-1306Crossref PubMed Scopus (243) Google Scholar). Although the BM structural role in defining tissue architecture and compartmentalization has long been recognized, its dynamic role in the modulation of cell behavior has only recently been documented (1Kalluri R. Nat. Rev. Cancer. 2003; 3: 422-433Crossref PubMed Scopus (1335) Google Scholar). Aberrant cancer cell interactions with BM proteins play a crucial role in the biology of metastasis (3Engbring J.A. Kleinman H.K. J. Pathol. 2003; 200: 465-470Crossref PubMed Scopus (188) Google Scholar). Cancer cells must be able to coordinately decrease cell-cell interactions and increase cell adhesion to an adjacent BM in order to become motile, which along with the capacity of degrading/remodeling a BM directly relates to their metastatic potential (4Stewart D.A. Cooper C.R. Sikes R.A. Reprod. Biol. Endocrinol. 2004; 2: 1-13Crossref PubMed Scopus (108) Google Scholar). This cell behavior is accompanied by changes in the expression and/or usage of various adhesion receptors, including integrins (5Edlund M. Miyamoto T. Sikes R.A. Ogle R. Laurie G.W. Farach-Carson M.C. Otey C.A. Zhau H.E. Chung L.W. Cell Growth Differ. 2001; 12: 99-107PubMed Google Scholar). Integrins are transmembrane adhesion receptors for ECM proteins that not only provide physical anchoring cell support but also play a pivotal role in triggering intracellular signaling in response to environmental changes through interactions with molecules such as growth factor receptor tyrosine kinases (6Goel H.L. Fornaro M. Moro L. Teider N. Rhim J.S. King M. Languino L.R. J. Cell Biol. 2004; 166: 407-418Crossref PubMed Scopus (75) Google Scholar, 7Goel H.L. Moro L. King M. Teider N. Centrella M. McCarthy T.L. Holgado-Madruga M. Wong A.J. Marra E. Languino L.R. Cancer Res. 2006; 66: 331-342Crossref PubMed Scopus (25) Google Scholar), MAPK/ERK 1/2 (8Juliano R. BioEssays. 1996; 18: 911-917Crossref PubMed Scopus (114) Google Scholar, 9Wei J. Shaw L.M. Mercurio A.M. J. Biol. Chem. 1998; 273: 5903-5907Abstract Full Text Full Text PDF PubMed Scopus (68) Google Scholar), and PI 3-kinase/AKT (10Shaw L.M. Rabinovitz I. Wang H.H. Toker A. Mercurio A.M. Cell. 1997; 91: 949-960Abstract Full Text Full Text PDF PubMed Scopus (547) Google Scholar, 11Downward J. Curr. Opin. Cell Biol. 1998; 10: 262-267Crossref PubMed Scopus (1188) Google Scholar). These various interactions help in modulating the expression of genes exerting stringent control upon cell survival, motility, and cell proliferation (12Hynes R.O. Trends Cell Biol. 1999; 9: M33-M37Abstract Full Text Full Text PDF PubMed Scopus (255) Google Scholar). Intracellular protein degradation via the ubiquitin-proteasome pathway is a prime pathway through which cells normally regulate processes involved in cell growth and proliferation (13Ciechanover A. Cell. 1994; 79: 13-21Abstract Full Text PDF PubMed Scopus (1599) Google Scholar, 14Almond J.B. Cohen G.M. Leukemia. 2002; 16: 433-443Crossref PubMed Scopus (471) Google Scholar). There is evidence that a number of growth inhibitory molecules and tumor suppressor proteins, such as p53, p21, p27, p130, the β1C integrin, and FOXO1, are preferentially degraded by the ubiquitin-proteasome system in carcinoma cells (14Almond J.B. Cohen G.M. Leukemia. 2002; 16: 433-443Crossref PubMed Scopus (471) Google Scholar, 15Cardozo T. Pagano M. Nat. Rev. Mol. Cell. Biol. 2004; 5: 739-751Crossref PubMed Scopus (884) Google Scholar, 16Moro L. Perlino E. Marra E. Languino L.R. Greco M. J. Biol. Chem. 2004; 279: 1692-1702Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar, 17Huang H. Regan K.M. Wang F. Wang D. Smith D.I. van Deursen J.M. Tindall D.J. Proc. Natl. Acad. Sci. U. S. A. 2005; 102: 1649-1654Crossref PubMed Scopus (428) Google Scholar). Furthermore, E3 ubiquitin ligase family members Skp2 and Mdm2 have been shown to play a role in prostate cancer development and progression (18Mamillapalli R. Gavrilova N. Mihaylova V.T. Tsvetkov L.M. Wu H. Zhang H. Sun H. Curr. Biol. 2001; 11: 263-267Abstract Full Text Full Text PDF PubMed Scopus (200) Google Scholar, 19Yang G. Ayala G. De Marzo A. Tian W. Frolov A. Wheeler T.M. Thompson T.C. Harper J.W. Clin. Cancer Res. 2002; 8: 3419-3426PubMed Google Scholar, 20Khor L.Y. Desilvio M. Al-Saleem T. Hammond M.E. Grignon D.J. Sause W. Pilepich M. Okunieff P. Sandler H. Pollack A. Cancer. 2005; 104: 962-967Crossref PubMed Scopus (50) Google Scholar). In a previous report, we provided evidence for a novel pathological mechanism whereby prostate carcinoma cell adhesion to collagen type I (COL1), a major ECM protein at osseous metastatic sites, promotes cancer cell proliferation through depletion of BRCA2 protein, the product of a tumor suppressor gene whose inactivation accounts for an increased risk in cancer development (21Venkitaraman A.R. Cell. 2002; 108: 171-182Abstract Full Text Full Text PDF PubMed Scopus (1402) Google Scholar, 22Liede A. Karlan B.Y. Narod S.A. J. Clin. Oncol. 2004; 22: 735-742Crossref PubMed Scopus (346) Google Scholar, 23Tavtigian S.V. Simard J. Rommens J. Couch F. Shattuck-Eidens D. Neuhausen S. Merajver S. Thorlacius S. Offit K. Stoppa-Lyonnet D. Belanger C. Bell R. Berry S. Bogden R. Chen Q. Davis T. Dumont M. Frye C. Hattier T. Jammulapati S. Janecki T. Jiang P. Kehrer R. Leblanc J.F. Mitchell J.T. McArthur-Morrison J. Nguyen K. Peng Y. Samson C. Schroeder M. Snyder S.C. Steele L. Stringfellow M. Stroup C. Swedlund B. Swense J. Teng D. Thomas A. Tran T. Tranchant M. Weaver-Feldhaus J. Wong A.K. Shizuya H. Eyfjord J.E. Cannon-Albright L. Tranchant M. Labrie F. Skolnick M.H. Weber B. Kamb A. Goldgar D.E. Nat. Genet. 1996; 12: 333-337Crossref PubMed Scopus (726) Google Scholar). This newly described effect resulted from β1 integrin-dependent activation of the PI 3-kinase pathway, which promoted BRCA2 ubiquitination and degradation in the proteasome (24Moro L. Arbini A.A. Marra E. Greco M. J. Biol. Chem. 2005; 280: 22482-22491Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar). In this study, we extended our investigations to elucidate the mechanisms by which β1 integrin signaling in prostate cancer cells resulted in BRCA2 protein degradation in the proteasome. We also provide evidence demonstrating that the BRCA2-associated trophic effect is not restricted to the osseous environment but is quite active in mediating cancer cell proliferation after interaction with BM proteins. Cell Culture—PNT1A cells (a human prostate normal cell line established by immortalization of normal adult prostate epithelial cells) and PC-3 cells (a human prostate carcinoma cell line derived from a bone metastasis) were kept in culture as described previously (16Moro L. Perlino E. Marra E. Languino L.R. Greco M. J. Biol. Chem. 2004; 279: 1692-1702Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar, 24Moro L. Arbini A.A. Marra E. Greco M. J. Biol. Chem. 2005; 280: 22482-22491Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar). Cell Adhesion—Cell adhesion assays to ECM proteins were carried out using 96-well tissue culture plates as described previously (24Moro L. Arbini A.A. Marra E. Greco M. J. Biol. Chem. 2005; 280: 22482-22491Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar). Plates were precoated with different concentrations of FN (3 μg/ml; Sigma), LN (10 μg/ml; Invitrogen), PLN (10 μg/ml; Sigma), or COL4 (10 μg/ml; Sigma) for 16 h at 4 °C. Coating with 10 μg/ml bovine serum albumin (Sigma) served as negative control. Adhesion to the BM matrix Matrigel (Sigma) was tested in 96-well plates coated with 50 μl/well of a 1:3 dilution in RPMI cell were in RPMI (Sigma) for at with in of RPMI bovine cell were to for h onto Matrigel or bovine serum albumin (10 at and were cells were in of 50 and in was in a Inhibition assays were by cells for h on in the of a to human β1 integrin or the a endothelial protein used as a negative control. were for and were onto FN (3 LN (10 PLN (10 or COL4 (10 and and protein were by as described previously (24Moro L. Arbini A.A. Marra E. Greco M. J. Biol. Chem. 2005; 280: 22482-22491Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar). cells were for h with or or the PI 3-kinase Sigma), (10 or or with the proteasome (10 were μg/ml 10 μg/ml to μg/ml to Skp2 μg/ml to Mdm2 μg/ml μg/ml 1/2 μg/ml μg/ml or dilution of of BRCA2 ubiquitination was as described previously (24Moro L. Arbini A.A. Marra E. Greco M. J. Biol. Chem. 2005; 280: 22482-22491Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar). BRCA2 with Skp2, cell were and with of to were with protein with 10 and were to by to were using μg/ml to Skp2 or μg/ml to BRCA2 the cell were with of to Skp2 and by and were using μg/ml or μg/ml to and with BRCA2 (a from M. C. of M. D. Cancer a negative of PI 3-kinase provided by R. of or were as described previously (24Moro L. Arbini A.A. Marra E. Greco M. J. Biol. Chem. 2005; 280: 22482-22491Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar). of for human Skp2, and was from and used for to the assays were in 96-well plates as described previously (24Moro L. Arbini A.A. Marra E. Greco M. J. Biol. Chem. 2005; 280: 22482-22491Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar). are as the was by the were at and to the of and PC-3 cells to LN, PLN, and COL4, major of BM, and to FN, a extracellular matrix protein R. K.M. J. Cell Sci. 2002; PubMed Scopus Google at the but a in shown in cells adhered to FN, to a to LN and PLN of FN and adhesion to metastatic PC-3 cells a with of adhesion to FN and newly adhesion to BM proteins. cell adhesion to FN, LN, COL4, and PLN K. J.A. J. Cell Biol. PubMed Scopus Google is by integrin receptors that a β1 subunit to FN, to LN, and to COL4, to we tested the effect of the β1 on cell shown in adhesion to FN was by and in and PC-3 cells, Adhesion to LN was inhibited by in and in PC-3 cells, adhesion to PLN was inhibited in cell and onto COL4 PC-3 cell adhesion was inhibited be onto BM we tested the of normal and cancer prostate cells to a BM H.K. Cancer Biol. 2005; PubMed Scopus Google Scholar). shown in PC-3 cells adhered to Matrigel in a that was inhibited by the normal prostate cell adhesion was in the Adhesion of PC-3 to BM BRCA2 in a β1 PC-3 cell adhesion to BM proteins a effect upon BRCA2 this and PC-3 cells were onto plates coated with FN, LN, PLN, COL4, or Matrigel and BRCA2 were in cells increased BRCA2 protein after adhesion to BM proteins onto FN after PC-3 cells (PLN) or COL4, of BRCA2 after adhesion for effect was onto COL4, which BRCA2 protein to decrease after only h by BRCA2 protein not after h of cell adhesion not β1 BRCA2 protein to after h onto COL4 as well as onto BM proteins not COL4 is the of the BM, of the were onto this BM BRCA2 after Cancer Cell Adhesion to BM the signaling cascade by BM proteins effect on cell proliferation, we of in and PC-3 cells onto various cell proliferation of the adhesion to COL4 PC-3 cell proliferation with by response was upon adhesion onto LN and PLN was onto FN not of PC-3 cells with inhibited the response to COL4 by and to LN and PLN by not These results were and onto BM shown in adhesion to Matrigel cell proliferation by and inhibited the response by increase in after adhesion to BM proteins be by PC-3 cells with BRCA2 In PC-3 cells were with BRCA2 or for after which we BRCA2 protein and upon h of cell adhesion to COL4 in the or of the proteasome BRCA2 protein increased with COL4 BRCA2 by in cells, but this effect in which at the the cells of BRCA2 protein upon adhesion to COL4, which resulted in a in This trophic effect be with the proteasome which by of cells with resulted in BRCA2 to Skp2 BRCA2 in PC-3 to it is that proteins Skp2 and Mdm2 the degradation of negative of cell proliferation in cancer H. Regan K.M. Wang F. Wang D. Smith D.I. van Deursen J.M. Tindall D.J. Proc. Natl. Acad. Sci. U. S. A. 2005; 102: 1649-1654Crossref PubMed Scopus (428) Google Scholar, Mol. Cell. 2002; 9: Full Text Full Text PDF PubMed Scopus Google Scholar, Y. W. Y. B. M.C. Nat. Cell Biol. 2001; 3: PubMed Scopus Google Scholar), we that were to be involved in BRCA2 ubiquitination and proteasomal degradation in prostate cancer We PC-3 cell adhesion to COL4 effect upon Skp2 or Mdm2 protein in PC-3 cell adhesion to COL4 triggered Skp2 and Mdm2 protein expression by 281 and at h and and at This effect was inhibited by a β1 for Skp2 but not We to of Skp2 or Mdm2 an effect upon BRCA2 protein and shown in Skp2 by resulted in Skp2 protein cell depletion and of BRCA2 protein after adhesion to COL4 Furthermore, newly changes of the new upon PC-3 cell adhesion to COL4 BRCA2 protein depletion was from increase in Mdm2 protein upon adhesion to COL4, and Mdm2 by not BRCA2 protein not Skp2 with we changes in Skp2 expression effect upon BRCA2 ubiquitination in PC-3 cells after COL4 this cell from PC-3 cells with Skp2 or were at various and with by with an ubiquitin adhesion PC-3 cells BRCA2 ubiquitination, as previously described (24Moro L. Arbini A.A. Marra E. Greco M. J. Biol. Chem. 2005; 280: 22482-22491Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar). h of adhesion to COL4, cells with increase in BRCA2 ubiquitination at a that the in BRCA2 protein shown in In of Skp2 expression resulted in a in BRCA2 ubiquitination at This effect results from a interaction the proteins as demonstrated by coimmunoprecipitation In the shown in after COL4 adhesion amounts of complex with increased from at h to amounts at h to decrease after BRCA2 protein This behavior the changes in Skp2 in BRCA2 was also when the was used for not PC-3 Cell Adhesion to BM PI in a β1 also the of the MAPK/ERK and the PI 3-kinase signaling in modulating BRCA2 protein depletion upon cancer cell adhesion to In with MAPK/ERK in PC-3 cells was at and not increase after adhesion to COL4 the PI 3-kinase increased by highly for as long as h as by with This response was on β1 integrin as with the resulted in in onto COL4 BRCA2 as demonstrated by of PI 3-kinase with or not which increased BRCA2 protein by after h of adhesion to of BRCA2 by Skp2 PI the increase in Skp2 protein leading to BRCA2 ubiquitination after PC-3 cell adhesion to COL4 results from PI 3-kinase we PC-3 cells with a negative of the PI 3-kinase adhesion to COL4 and protein of Skp2, and complex and in with prevented BRCA2 protein degradation and Skp2 protein up-regulation as well as the increase in protein complex and upon cell adhesion to of carcinoma in to the epithelial BM and the has long the progression to carcinoma F. Google Scholar). In for and metastasis to carcinoma cells must be able to and and of which are from the adjacent by of a interaction of carcinoma cells with BM proteins must be at the of their metastatic that normal PNT1A, highly PC-3 carcinoma cells adhesion onto the main of the BM as well as on a BM matrix the the ECM FN at the and a of BM was a for PC-3 cells when with normal This latter be with the expression of the FN receptor integrin in PC-3 when with crucial is that after adhesion to isolated BM proteins, to COL4, highly carcinoma cells a in a of new and cell proliferation. This trophic response to be by β1 integrin as a was previously demonstrated onto a for β1 integrin receptors (24Moro L. Arbini A.A. Marra E. Greco M. J. Biol. Chem. 2005; 280: 22482-22491Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar). response after adhesion to LN and PLN was with COL4, and effect was onto to onto the BM matrix prostate cancer cells a proliferation that was with isolated various proteins in response PC-3 cell adhesion onto BM was to a sustained BRCA2 protein depletion and be by BRCA2 This pathway to cell proliferation on and on a of BRCA2 protein, as by the to in BRCA2 protein after PC-3 cell adhesion to normal cell adhesion to FN resulted in an increase in BRCA2 expression with effect upon to an of evidence that BRCA2 also as modulator of cell proliferation and tumor previous that BRCA2 in the cell line resulted in decrease in when S.C. R. Zhang S. M.C. Cancer Res. 2002; Google Scholar). Miyamoto H. T. K. H. H. S. 2004; PubMed Scopus Google that cells an increased proliferation after adhesion to mechanisms involved are not well of the response to the activation of an that cell progression and/or in response to amounts of a complex BRCA2 L.Y. T. S.A. Proc. Natl. Acad. Sci. U. S. A. 1998; PubMed Scopus Google Scholar, K. Jiang Couch J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar, L. J. W. A.J. Proc. Natl. Acad. Sci. U. S. A. 2005; 102: PubMed Scopus Google Scholar). of this mechanism our β1 integrin signaling and Mdm2 and an pathway Skp2 Furthermore, PC-3 cells in the gene 2004; PubMed Scopus Google Scholar, G. J. M. J. Cancer. 1994; PubMed Scopus Google Scholar). of BRCA2 protein upon cancer cell adhesion to BM proteins and osseous (24Moro L. Arbini A.A. Marra E. Greco M. J. Biol. Chem. 2005; 280: 22482-22491Abstract Full Text Full Text PDF PubMed Scopus (25) Google through protein degradation in the proteasome. the mechanisms involved not been In the study, we have provided evidence that this is by Skp2, an protein that associates with and to the ubiquitin ligase complex Mol. Cell. 2002; 9: Full Text Full Text PDF PubMed Scopus Google Scholar). down-regulation of Skp2 by was to BRCA2 the in cell proliferation upon cancer cell adhesion to that this mechanism may be in prostate cancer has also been provided in on that that Skp2 and increase in and prostate carcinoma G. Ayala G. De Marzo A. Tian W. Frolov A. Wheeler T.M. Thompson T.C. Harper J.W. Clin. Cancer Res. 2002; 8: 3419-3426PubMed Google Scholar). in Skp2 are upon β1 integrin-mediated signaling for Skp2 and BRCA2 degradation be prevented by a β1 demonstrating that cell adhesion to the ECM results in Skp2 and protein up-regulation been provided previously A.C. Pagano M. J. Cell Biol. 2001; PubMed Scopus Google Scholar). We results and for the that β1 integrin-mediated signaling is for changes in Skp2 up-regulation of Skp2 that β1 integrin adhesion is through PI 3-kinase/AKT and be by a negative of PI These are in with PI 3-kinase in degradation of and H. Regan K.M. Wang F. Wang D. Smith D.I. van Deursen J.M. Tindall D.J. Proc. Natl. Acad. Sci. U. S. A. 2005; 102: 1649-1654Crossref PubMed Scopus (428) Google Scholar, R. Gavrilova N. Mihaylova V.T. Tsvetkov L.M. Wu H. Zhang H. Sun H. Curr. Biol. 2001; 11: 263-267Abstract Full Text Full Text PDF PubMed Scopus (200) Google Scholar, E. E. C. J.A. C. J. J. C. F. I. Cancer Res. 2005; PubMed Scopus Google Scholar, J. 2006; 66: PubMed Scopus Google Scholar). of PI 3-kinase/AKT in BRCA2 protein depletion was not as activation of this pathway has been in on cancer cell proliferation and P. T. 2001; PubMed Scopus Google Scholar, M. D.A. T. R. Clin. Cancer Res. 2002; 8: Google Scholar, N. Zhang Jiang Res. 2003; PubMed Scopus Google Scholar, D.A. S. Cancer Res. 2004; PubMed Scopus Google Scholar). evidence for increased PI 3-kinase/AKT in prostate and at the of prostate carcinoma has been by protein with L. Chen T. J.W. 2001; PubMed Scopus Google Scholar). our have demonstrated that Skp2 directly with and promotes the degradation of in this process PI 3-kinase/AKT activation by β1 integrin-mediated signaling cancer cell interaction with BM proteins, a crucial at the of the metastatic cascade to and Furthering the understanding of this molecular pathway may prove valuable in designing new therapeutic strategies aimed at modifying the natural history of prostate carcinoma. We M. C. for the BRCA2 and R. for the PI 3-kinase