Expression of human kinase suppressor of Ras 2 (hKSR-2) gene in HL60 leukemia cells is directly upregulated by 1,25-dihydroxyvitamin D(3) and is required for optimal cell differentiation.
Induction of terminal differentiation of neoplastic cells offers potential for a novel approach to cancer therapy. One of the agents being investigated for this purpose in preclinical studies is 1,25-dihydroxyvitamin D(3) (1,25D), which can convert myeloid leukemia cells into normal monocyte-like cells, but the molecular mechanisms underlying this process are not fully understood. Here, we report that 1,25D upregulates the expression of hKSR-2, a new member of a small family of proteins that exhibit evolutionarily conserved function of potentiating ras signaling. The upregulation of hKSR-2 is direct, as it occurs in the presence of cycloheximide, and occurs primarily at the transcriptional level, via activation of vitamin D receptor, which acts as a ligand-activated transcription factor. Two VDRE-type motifs identified in the hKSR-2 gene bind VDR-RXR alpha heterodimers present in nuclear extracts of 1,25D-treated HL60 cells, and chromatin immunoprecipitation assays show that these VDRE motifs bind VDR in 1,25D-dependent manner in intact cells, coincident with the recruitment of RNA polymerase II to these motifs. Treatment of the cells with siRNA to hKSR-2 reduced the proportion of the most highly differentiated cells in 1,25D-treated cultures. These results demonstrate that hKSR-2 is a direct target of 1,25D in HL60 cells, and is required for optimal monocytic differentiation.
Wang
Xuening
X
Department of Pathology and Laboratory Medicine, UMDNJ-New Jersey Medical School, 185 South Orange Avenue, C-543, Newark, NJ 07103, USA.
Wang
Tian-Tian
TT
White
John H
JH
Studzinski
George P
GP
D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D002117:Calcitriol / Q000031:analogs & derivatives / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology*; D015972:Gene Expression Regulation, Neoplastic; D018922:HL-60 Cells / Q000502:physiology*; D006801:Humans; D009000:Monocytes / Q000502:physiology; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D012319:RNA Polymerase II / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D018167:Receptors, Calcitriol / Q000037:antagonists & inhibitors / Q000378:metabolism; D020218:Response Elements; D015854:Up-Regulation
D015415:Biomarkers; D034741:RNA, Small Interfering; D018167:Receptors, Calcitriol; C410228:ZK159222; D011494:Protein Kinases; C097199:KSR-1 protein kinase; D012319:RNA Polymerase II; D002117:Calcitriol