Designed FHIT alleles establish that Fhit-induced apoptosis in cancer cells is limited by substrate binding.
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Trapasso F, Krakowiak A, Cesari R, Arkles J, Yendamuri S, Ishii H, Vecchione A, Kuroki T, Bieganowski P, Pace HC, Huebner K, Croce CM, Brenner C
Designed FHIT alleles establish that Fhit-induced apoptosis in cancer cells is limited by substrate binding.
Proc Natl Acad Sci U S A. 2003 Feb 18;100(4):1592-7. Epub 2003 Feb 6.
- PubMed ID
- 12574506 [ View in PubMed]
- Abstract
The FHIT gene is inactivated early in the development of many human tumors, and Fhit-deficient mice have increased cancer incidence. Viral reexpression of Fhit kills Fhit-deficient cells by induction of apoptosis. Fhit, a member of branch 2 of the histidine-triad superfamily of nucleoside monophosphate hydrolases and transferases, is a diadenosine polyphosphate hydrolase, the active-site histidine of which is not required for tumor suppression. To provide a rigorous test of the hypothesis that Fhit function depends on forming a complex with substrates, we designed a series of alleles of Fhit intended to reduce substrate-binding andor hydrolytic rates, characterized these mutants biochemically, and then performed quantitative cell-death assays on cancer cells virally infected with each allele. The allele series covered defects as great as 100,000-fold in k(cat) and increases as large as 30-fold in K(M). Nonetheless, when mutant FHIT genes were expressed in two human cancer cell lines containing FHIT deletions, reductions in apoptotic activity correlated exclusively with K(M). Mutants with 2- and 7-fold increases in K(M) significantly reduced apoptotic indices, whereas the mutant with a 30-fold increase in K(M) retained little cellular function. These data indicate that the proapoptotic function of Fhit is limited by substrate binding and is unrelated to substrate hydrolysis.