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

Abstract

Summary. The downstream effects of p15 and p16 gene deletions and loss of transcripts on dihydrofolate reductase (DHFR) were examined in 63 B-precursor (BP) acute lymphoblastic leukaemia (ALL) samples. p15 and/or p16 gene deletions were seen in 6% and 8%, respectively, of BP-ALL samples; however, losses of p15 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 that lacked p15 and/or p16 transcripts, only six (23%) exhibited low levels of DHFR by flow cytometry assay with Pt430, a fluorescent anti-folate. Conversely, 18 out of 37 (49%) BP-ALL samples with intact p15 and/or p16 genes and transcripts showed low levels of DHFR (P 0´04). In p15-and p16-null K562 cells transfected with a tetracycline-inducible p15 cDNA construct, induction of p15 transcripts and protein was accompanied by decreased growth rates, decreased S-phase fraction, decreased retinoblastoma protein phosphorylation, and markedly reduced levels of DHFR transcripts and protein.Collectively, our results suggest that losses of p15 and/or p16 gene expression result in elevated levels of DHFR in BP-ALL in children. However, additional downstream factors undoubtedly also contribute to elevated levels of this enzyme target.

Prognostic Role of the Reduced Folate Carrier, the Major Membrane Transporter for Methotrexate, in Childhood Acute Lymphoblastic Leukemia: A Report from the Children's Oncology Group

“…As described herein, our results strongly suggest a uniquely prognostic role for the human reduced folate carrier (hRFC), the major transport protein for methotrexate in pediatric ALL (20). Results for hRFC were confirmed in a separate casecontrol BP-ALL population from an earlier study (21). This surprising result further documents the critical role that methotrexate plays in ALL therapy and strongly validates our previous studies of hRFC transcriptional and posttranscriptional regulation in this disease (22,23).…”

“…When we assayed hRFC transcripts in a separate case-control cohort of 26 BP-ALL patients treated on a single clinical protocol from our earlier study (21), essentially identical results were obtained to those from the larger group of patients treated on multiple protocols. This establishes the generality of our findings in pediatric BP-ALL and also shows that these associations between hRFC expression and treatment outcome are not treatment protocol-dependent.…”

“…As validation of our finding that hRFC transcript levels directly correlated with chemotherapy outcome in BP-ALL patients treated with methotrexate, we studied RNAs isolated from a separate cohort of BP-ALL patients treated with POG 8602 from our earlier study (21), for which cases (n = 14) and controls (n = 12) were matched by risk groups and treatment arms. In this study group, total hRFC transcripts were again significantly increased in the controls compared with the cases (increase of 3.84-fold, by median values; P = 0.0221; Fig.…”

“…Ninety-one of these samples were usable, including 42 cases and 49 controls. (b) Twenty-six diagnostic specimens were from our earlier study (21), including controls (n = 12) and cases (n = 14) from patients treated on the POG 8602 protocol, in which total RNAs were available. Patient cohort b had no overlap with patients from POG 8602 in cohort a.…”

A hagyományos citogenetika és a FISH egymást jól kiegészítő vizsgálatok gyermekkori akut limfoid leukémiában

“…Az eddigi irodalmi adatok a deléció prognosztikai hatásával kapcsolatosan ellentmondásosak (23), ami azzal állhat összefüggésben, hogy a deléciós státusz a sejtek kemoterápiás szerekkel szembeni érzékenységét is befolyásolja (6,44). A deléció gyakran társul hátrá-nyos klinikai adatokkal (magas fehérvérsejtszám, T-immunfenotípus, mediasztinális érintett ség), ilyenkor az eseménymentes túlélési ráta az átlagosnál rövidebb (14).…”