Plexin Bl is downregulated in renal cell carcinomas and modulates cell growth

Plexins are a family of transmembrane receptors that interact with the repulsive axon guidance molecules (Semaphorins) in neural tissues. In extraneural tissues, plexins are involved in other cellular functions often altered in neoplastic cells, such as adhesion, migration, and apoptosis. Plexin Bl has been implicated in the regulation of Akt, which is an activated pathway in renal cell neoplasms, and only I report has emphasized its role as an oncogenic factor. Furthermore, plexin Bl is located in 3p2l, which is a chromosomal region deleted frequently in renal cell carcinomas. In accordance with a hypothetical oncogenic role for plexin Bl, we have shown by reverse transcription-polymerase chain reaction that plexin Bl is expressed in nonneoplastic renal tissue, and it is severely downregulated in clear cell renal carcinomas. We have also demonstrated by immunohistochernistry on tissue microarrays that plexin Bl protein is absent in more than 80% of renal cell carcinomas (1169 in 209 carcinomas examined). Otherwise, all kinds of renal tubules showed strong membrane reactivity. Moreover, when we have induced plexin Bl expression with an expression vector in the renal adenocarcinoma cell line ACHN, a marked reduction in proliferation rate was produced. Altogether, this evidence suggests a possible role for plexin Bl in renal oncogenesis.