ALTERATIONS OF CYCLIN-DEPENDENT KINASE-4 INHIBITOR (P16(INK4A) MTS1) GENE STRUCTURE AND EXPRESSION IN ACUTE LYMPHOBLASTIC LEUKEMIAS/

The cyclin-dependent kinase 4 (cdk4) inhibitor (p16(INK4)/MTS1/ CDKN2) gene has been recently identified as a putative tumor suppressor gene because of the high frequency of homozygous deletion observed in nume rous human tumor cell lines, including leukemias. However, results obt ained from uncultured tumor samples have led to discussion of the rele vance of these findings. Using reverse transcriptase polymerase chain reaction (RT-PCR) and Southern blot analysis, we have investigated p16 (INK4A) gene at both RNA and genomic levels in various types of leukem ias: acute myeloid leukemia (AML) (n = 23); acute lymphocytic leukemia (ALL) (n = 22) and B cell chronic lymphoproliferative disorders (CLPD ) (n = 33). p16(INK4A) mRNA expression was not found in only 1/20 AML and 2/23 CLPD samples. Conversely, p16(INK4A) mRNA was not detected in 5/17 ALL cases, and intensity of PCR products were barely detectable in seven additional cases, possibly related to the contamination by no rmal cells in some cases. By Southern blotting, a homozygous deletion of p16(INK4A) gene was found in 6/17 ALL cases (35%) among which 4/6 w ere negative or weakly positive by RT-PCR assay. None of the five AML and 20 CLL samples studied had p16(INK4A) deletion. Sequence analysis of p16(INK4A) exon 2 did not show point mutation in two of these cases lacking mRNA expression. Our data provide further evidence that among hematological malignancies, ALL are the most likely to be associated with p16(INK4A) inactivation, mainly by homozygous gene deletion. Sinc e most hematological malignancies - except ALL - are infrequently asso ciated with p16(INK4A) and retinoblastoma (Rb) gene alteration it seem s worthwhile to explore cdk4 and cdk6 expression to determine whether or not the disruption of the p16(INK4A)/Rb/cdk4/cdk6 regulatory loop m ight play a role in their pathogenesis.