Implication of a protein-tyrosine-phosphatase in human lung cancer.

Protein tyrosyl phosphorylation plays an essential role in regulating cellular events such as proliferation, differentiation and oncogenesis. The recent characterization of the family of protein tyrosine phosphatases (PTPases) suggests that dephosphorylation might be a crucial event in these phenomena. One of the functions of PTPases is to reverse the effect of protein tyrosine kinases (PTKases), many of which are oncogenes, suggesting that they may act as tumor suppressors as described for HPTP gamma. In order to investigate the implication in lung cancer of HPTP beta, a receptor PTPase, we have developed a semi-quantitative method derived from primer-directed reverse transcription (RT) and subsequent polymerase chain reaction (PCR) with 32P-labelled nucleotide. We have demonstrated that the expression of HPTP beta mRNA was dramatically decreased in lung adenocarcinomas and lung malpighian carcinomas as compared to normal lung tissue. In addition, HPTP beta was not expressed in the pulmonar adenocarcinoma cell line A427, which proliferates in a deregulated way. These results suggest that the loss of expression of HPTP beta might play a role in neoplasic transformation and thus this molecule could act as a tumor suppressor factor.