Relationship of p15 and p16 gene alterations to elevated dihydrofolate reductase in childhood acute lymphoblastic leukaemia

The downstream effects of p15 and p16 gene deletions and loss of transcript s on dihydrofolate reductase (DHFR) were examined in 63 B-precursor (BF) ac ute lymphoblastic leukaemia (ALL) samples. p15 and/or p16 gene deletions we re seen in 6% and 8%, respectively, of BP-ALL samples; however, losses of p 15 and/or p16 transcripts were seen in 26 out of 63 (41%) samples. Loss of p15 transcripts (36.5%)exceeded that for p16 (17.5%). For the 26 BP-ALLs th at lacked p15 and/or p16 transcripts, only six (23%) exhibited low levels o f DHFR by flow cytometry assay with Pt430, a fluorescent anti-folate. Conve rsely, 18 out of 37 (49%) BP-ALL samples with intact pi and/or p16 genes an d transcripts showed low levels of DHFR (P = 0.04). In p15- and p16-null K5 62 cells transfected with a tetracycline-inducible p15 cDNA construct, indu ction of p15 transcripts and protein was accompanied by decreased growth ra tes, decreased S-phase fraction, decreased retinoblastoma protein phosphory lation, and markedly reduced levels of DHFR transcripts and protein. Collec tively, our results suggest that losses of pi and/or p16 gene expression re sult in elevated levels of DHFR in BP-ALL in children, However, additional downstream factors undoubtedly also contribute to elevated levels of this e nzyme target.