Reduced folate carrier gene expression in childhood acute lymphoblastic leukemia: relationship to immunophenotype and ploidy.
Reduced folate carrier (RFC) transcripts in human leukemias were measured by a competitive PCR assay. Total RNAs were reverse transcribed and amplified in the presence of competitive templates for RFC and beta-actin. RFC transcripts were normalized to transcripts for beta-actin. In a series of K562 sublines, a approximately 30-fold range of RFC transcripts measured by PCR assay closely agreed with results of Northern analysis and varied in proportion to RFC protein on Western blots and [3H]methotrexate transport. RFC transcripts varied over a 88-fold range in 49 specimens from 48 children with acute lymphoblastic leukemia (ALL). Median RFC transcripts were similar for 15 T-cell and 33 B-precursor ALL samples (RFC/beta-actin = 6.13 x 10(-3) and 7.92 x 10(-3), respectively) and for 41 diagnostic (7.20 x 10(-3)) and 8 relapse (5.58 x 10(-3)) samples. Whereas PCR measurements of RFC transcripts approximated changes in methotrexate transport in B-precursor ALL blasts (n = 10), for T-ALL blasts (n = 12) there was no apparent relationship between these parameters. For hyperdiploid B-precursor blasts (n = 11) with greater than 52 chromosomes and three to five copies of chromosome 21, the median RFC transcript level was approximately 3-fold higher than that for diploid B-precursor blasts. RFC transcripts were also elevated for two of three B-precursor specimens with acquired trisomy 21. Our results suggest that RFC gene expression is far more predictive of methotrexate uptake capacity in B-precursor than T-ALL and that increased copies of chromosome 21 in B-precursor ALL blasts are generally associated with increased RFC transcripts. Hence, the good prognosis for children with hyperdiploid B-precursor ALL treated with antimetabolite-based chemotherapy and the high levels of methotrexate and methotrexate polyglutamates accumulated may, in part, reflect elevated RFC gene expression and capacities for methotrexate transport.
Zhang
L
L
Experimental and Clinical Therapeutics Program, Barbara Ann Karmanos Cancer Institute, Detroit, MI 48201, USA.
Taub
J W
JW
Williamson
M
M
Wong
S C
SC
Hukku
B
B
Pullen
J
J
Ravindranath
Y
Y
Matherly
L H
LH
D000293:Adolescent; D000595:Amino Acid Sequence; D000964:Antimetabolites, Antineoplastic / Q000493:pharmacokinetics; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000235:genetics; D002648:Child; D002675:Child, Preschool; D005260:Female; D015870:Gene Expression; D006801:Humans; D016130:Immunophenotyping; D007223:Infant; D020014:K562 Cells / Q000378:metabolism / Q000473:pathology; D015458:Leukemia, T-Cell / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D008297:Male; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D008727:Methotrexate / Q000493:pharmacokinetics; D008969:Molecular Sequence Data; D011003:Ploidies; D015452:Precursor B-Cell Lymphoblastic Leukemia-Lymphoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D058978:Reduced Folate Carrier Protein; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014316:Tritium; D014407:Tumor Cells, Cultured
D000964:Antimetabolites, Antineoplastic; D002352:Carrier Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D058978:Reduced Folate Carrier Protein; C548699:SLC19A1 protein, human; C120043:SLC19A2 protein, human; D014316:Tritium; D008727:Methotrexate