PROTEIN EXPRESSION AND FUNCTIONAL-ANALYSIS OF THE FHIT GENE IN HUMAN TUMOR-CELLS

Background: The fragile histidine triad (FHIT) gene at chromosome 3p14 .2 has been proposed to be a candidate tumor suppressor gene in human cancers, To test whether FHIT exhibits the functional properties of a tumor suppressor gene, we studied the expression of its protein (pFHIT ) in human carcinoma cells and examined the ability of FHIT to inhibit the neoplastic phenotype of cancer cells, Methods: Subcellular locali zation and patterns of protein expression in tumor cells were determin ed by immunohistochemical analysis and immunoblotting with the use of polyclonal anti-pFHIT antisera, In tumor cells with undetectable pFHIT , we examined the effect of recombinant pFHIT expression on morphology , growth rate, colony formation, and in vivo tumor formation, Results: We demonstrated that pFHIT is a cytoplasmic 17-kd polypeptide whose e xpression could not be detected in 30 of 52 human carcinoma cell lines tested, We observed, however, that the stable overexpression of pFHIT did not alter cell morphology, inhibit colony formation, or inhibit c ell proliferation in vitro, Furthermore, overexpression of pFHIT did n ot lead to altered cell cycle kinetics in dividing cells, The in vivo tumorigenicity of a tumor cell line that expressed high levels of reco mbinant pFHIT was equivalent to that of control transfectants and of p arental cells, Conclusions: These results suggest that the replacement of pFHIT in human carcinoma cells does not suppress tumor cell growth and that this protein may be involved in tumorigenesis in ways that a re distinct from the ''classic'' tumor suppressor paradigm.