title: Constitutive expression of cellular retinoic acid binding protein II and lack of correlation with sensitivity to all-trans retinoic acid in acute promyelocytic leukemia cells.
abstract: The up-regulation of cellular retinoic acid binding protein-II (CRABP-II) has been invoked as an important mechanism of clinically acquired resistance to all-trans retinoic acid (RA) therapy in acute promyelocytic leukemia (APL). To test this hypothesis, we used quantitative reverse transcription-PCR and fast performance liquid chromatography procedures to examine the levels of CRABP-II mRNA and RA binding activity in APL patient samples. We found that CRABP-II mRNA in APL cells from pretreatment patients (n = 36) was constitutively expressed at relatively high levels (median, 0.92; range, 0.16-4.13) relative to the level in CRABP-H protein-expressing NB4 cells (arbitrarily set at 1.0 unit). Consistent with this finding, the RA binding activity of CRABP in APL cells from three pretreatment cases (range, 27.2-53.2 fmol/mg protein) was similar to that of NB4 cells (22.6 +/- 5.4 fmol/mg protein). Furthermore, in the pretreatment samples, there was no association between CRABP-H mRNA expression level and APL cellular sensitivity to RA-induced differentiation in vitro. After 45 days of remission induction therapy on Eastern Cooperative Oncology Group protocol E2491, CRABP-II mRNA was modestly increased from day 0 values in patients treated with either RA (median increase, 0.41) or chemotherapy (median increase, 0.56), and there was no significant difference between the two treatment groups (P = 0.91). In patients studied after relapse from RA therapy (n = 7), there was a significant decline in APL cell sensitivity to RA-induced differentiation in vitro compared with patients after relapse from chemotherapy (n = 5; P = 0.015-0.055 at three RA concentrations tested), but in the RA relapse cases, there was no change from pretreatment levels of CRABP-II mRNA (median, 0.98) or, in three relapse cases studied, of RA protein binding activity (range, 22.1-70.7 fmol/mg protein). Taken together, our data strongly imply that variations in CRABP-II expression and RA binding activity are not causally related to the development of clinically acquired APL cellular RA resistance, but rather, they suggest that constitutive expression of CRABP-II could have a facilitative role in the response of APL cells to RA.
authors.affiliation: Department of Oncology, Montefiore Medical Center and Albert Einstein Cancer Center, Bronx, New York 10467, USA.
authors.forename: D C
authors.initials: DC
authors.lastname: Zhou
authors.forename: S J
authors.initials: SJ
authors.lastname: Hallam
authors.forename: S J
authors.initials: SJ
authors.lastname: Lee
authors.forename: R S
authors.initials: RS
authors.lastname: Klein
authors.forename: P H
authors.initials: PH
authors.lastname: Wiernik
authors.forename: M S
authors.initials: MS
authors.lastname: Tallman
authors.forename: R E
authors.initials: RE
authors.lastname: Gallagher
mesh_terms: D002454:Cell Differentiation; D019008:Drug Resistance, Neoplasm; D018922:HL-60 Cells; D006801:Humans; D015473:Leukemia, Promyelocytic, Acute / Q000188:drug therapy* / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D018168:Receptors, Retinoic Acid / Q000378:metabolism*; D012074:Remission Induction; D014212:Tretinoin / Q000378:metabolism / Q000627:therapeutic use*
chemical_list: D012333:RNA, Messenger; D018168:Receptors, Retinoic Acid; C082928:retinoic acid binding protein II, cellular; D014212:Tretinoin