Antileukemic roles of human phospholipid scramblase 1 gene, evidence from inducible PLSCR1-expressing leukemic cells

Abstract

Phospholipid scramblase 1 (PLSCR1) is a multiply palmitoylated protein which is localized in either the cell membrane or nucleus depending on its palmitoylated state. The increasing evidence showed the biological roles of PLSCR1 in cell signaling, maturation and apoptosis. To investigate the functions of PLSCR1 in leukemic cells, we generated an inducible PLSCR1-expressing cell line using myeloid leukemic U937 cells. In this cell line, PLSCR1 was tightly regulated and induced upon tetracycline withdrawal. Our results showed that inducible PLSCR1 expression arrested the proliferation of U937 cells at G 1 phase. Meanwhile, PLSCR1-overexpressing U937 cells also underwent granulocyte-like differentiation with increased sensitivity to etoposide-induced apoptosis. Furthermore, we also found that PLSCR1 induction increased cyclin-dependent kinase inhibitors p27Kip1 and p21Cip1 proteins, together with downregulation of S phase kinase-associated protein 2 (SKP2), an F-box subunit of the ubiquitin-ligase complex that targets proteins for degradation. Additionally, PLSCR1 induction significantly decreased c-Myc protein and antiapoptotic Bcl-2 protein. Although the exact mechanism by which PLSCR1 regulates these cellular events and gene expression remains unresolved, our results suggest that PLSCR1 plays the antagonistic role regarding leukemia development. These data will shed new insights into understanding the biochemical and biological functions of PLSCR1 protein.

Wogonoside induces cell cycle arrest and differentiation by affecting expression and subcellular localization of PLSCR1 in AML cells

“…36 Moreover, induction of PLSCR1 expression arrested proliferation at the G 1 phase and prompted differentiation toward granulocyte-like cells of myeloid leukemic U937 cells (U937 plscr1 cells). 32 These results demonstrated that PLSCR1 expression could be induced during wogonoside-induced differentiation of AML-derived cell lines (U937 and HL-60). Wogonoside also increased PLSCR1 mRNA levels through transcriptional control, which could be blocked by the transcription inhibitor actinomycin D. Exogenous transfection of PLSCR1 siRNA into the cells reduced their differentiation, as well as G 1 phase arrest, in the presence of wogonoside.…”

Hypoxia-inducible factor-1α-induced differentiation of myeloid leukemic cells is its transcriptional activity independent

“…Such a system presented the advantage of not having been directly selected for the expression of the targeted gene during its establishment. As such, it had not been preselected with the possible particular features before the induced expression of the targeted protein, as described previously (Boer et al, 1998;Huang et al, 2006). In U937T pool and U937T clone cell lines, HIF-1a expression was tightly regulated and induced upon tetracycline withdrawal at both mRNA and protein levels, although a little leakage of expression could be seen.…”

The downregulation of onzin expression by PKCɛ-ERK2 signaling and its potential role in AML cell differentiation

“…36 Earlier, we also showed that ATRA and PMA activated PKCd to upregulate PLSCR1, which presents an anti-leukemic effect by contributing its differentiation. 2,37 More recently, the activation of PKCe and ERK signaling pathway is involved in myeloid lineage commitment. 27,38 ERK signaling may have an important role in PMA-and ATRA-induced leukemia cell differentiation.…”