Experimental models of prostate cancer research.

The Pathology B study section sponsored a one-day workshop focusing on new experimental models of prostate cancer research and preceded the International Conference on Prostate Cancer Research in Iowa City, Iowa. The workshop began with a discussion of the integrin-mediated modulation of prostate cancer proliferation and motility by Lucia R. Languino (Yale University, New Haven, CT). Interactions between (cancer) cells and the extracellular matrix are largely mediated by integrins, which have also emerged as key regulators of cell proliferation, migration, and intracellular signaling. β1C and β3 integrins may act as “growth or motility modulators” in prostate cells and play a role in modulating downstream intracellular signaling events. The β1C integrin is expressed in nonproliferative, differentiated benign prostatic epithelium and is down-regulated in prostatic adenocarcinoma, as well as in hyperplastic prostate glands. The β1C integrin is an alternatively spliced variant of the β1A subunit that, in contrast to β1A, inhibits fibroblast and epithelial cell proliferation. To investigate whether β1C plays a role in prostate epithelial cell proliferation, the prostatic carcinoma cell line PC3 was transfected with an inducible system with either β1C or β1A cytoplasmic tails and normal epithelial cell transfectants expressing β1C. In contrast to β1A, expression of β1C or its cytoplasmic domain completely inhibited thymidine incorporation by serum stimulation. Further results point to β1C as an upstream regulator of the cell cycle inhibitor p27kip1 expression. Immunohistochemical and immunoblotting analysis of human prostate epithelial cells reveal that β1C is co-expressed with p27kip1, the loss of which correlates with poor prognosis in prostate cancer. In vitro, increased levels of p27kip1 and inhibition of cyclin A-dependent kinase activity were observed in normal prostate epithelial cells upon expression of β1C. These data show that p27kip1 is a key downstream effector of β1C, in that β1C inhibitory activity on cell proliferation is completely prevented by p27kip1 antisense (but not mismatch) oligonucleotides. In parallel studies, a role for the αvβ3 integrin in the regulation of prostate cancer cell functions has been identified. Specifically, αvβ3 is expressed in primary cultures of prostate cancer epithelial cells, whereas it is undetectable in normal prostate epithelial cells; and αvβ3 mediates prostate cancer epithelial cell migration on β3 integrin substrates, such as vitronectin, an αvβ3 ligand expressed in mature bone where prostate cancer cells preferentially metastasize. Exogenous expression of αvβ3 induces LNCaP cells to adhere to and migrate on vitronectin. In response to αvβ3 engagement, increased tyrosine phosphorylation of focal adhesion kinase (FAK), a signaling molecule activated by integrins and able to modulate cell migration, is detected. Transfection of FAK-related non-kinase (FRNK), known to compete with FAK for its correct localization and phosphorylation, causes inhibition of β3-LNCaP cell migration, specifically on vitronectin. The study of the pathophysiological relevance of β1C and β3 integrin downstream effectors is likely to yield new insights into the mechanisms that contribute to prostate cancer progression and metastatic spread.