Involvement of the tyrosine phosphatase early gene of liver regeneration (PRL–1) in cell cycle and in liver regeneration and fibrosis effect of halofuginone

Abstract

Tyrosine phosphatase PRL-1 is one of the immediate-early genes up-regulated during liver regeneration and is apparently involved in cell proliferation. Previously, we have demonstrated that halofuginone, an inhibitor of collagen type I synthesis, prevents liver fibrosis and improves cirrhotic liver regeneration. In this study, we evaluated the effect of halofuginone on PRL-1 expression, its cellular localization in vitro and during liver regeneration, and fibrosis progression in vivo. In culture, halofuginone increased PRL-1 expression in primary rat hepatocytes and in hepatocellular carcinoma (HCC) cell lines, the former being more sensitive to halofuginone. The halofuginone-dependent increase in PRL-1 gene expression was correlated with an increase in the transcription factor early growth response-1 (Egr-1) and inversely correlated with the inhibition of cell proliferation. Halofuginone arrested HepG2 and Huh7 cell lines at the G1 phase, whereas Hep3B cells were arrested at G2/M, probably because of a reduction in the synthesis of cyclins D1 and B1 in all HCC cells and increased cyclin A in Hep3B cells. Halofuginone also affected the PRL-1 sub-cellular localization that was cell-cycle-dependent. In addition, halofuginone augmented PRL-1 expression in the remnant liver after partial hepatectomy and in chemically induced fibrosis in rats; this was accompanied by increased expression of insulin-like growth factor binding protein 1 (IGFBP-1), another immediate-early gene of regeneration. The regulation of the expression of the early genes of regeneration such as PRL-1 and IGFBP-1 is thus part of the mode of action of halofuginone and results in the prevention of liver fibrosis and improved cirrhotic liver regeneration.

Gene expression during chemically induced liver fibrosis: effect of halofuginone on TGF-β signaling

“…6), which plays a major role in HSC activation. Moreover, OPN, which is under the direct regulation of Smad3 (Shi et al 2001), augments collagen synthesis and the proliferation and migration of HSCs (Lee et al 2004), all of which are inhibited by halofuginone (Gnainsky et al 2003(Gnainsky et al , 2006. The increase in Cytoglobin/STAP synthesis that has been hypothesized to regulate collagen synthesis (Schmidt et al 2004) by activated HSCs under the control of TGF-β (Kawada et al 2001;Nakatani et al 2004), is prevented by halofuginone at a later stage of fibrosis ( Fig.…”

“…At a later stage, it affects genes involved in the cell cycle, i.e., cell development and differentiation, proliferation, and apoptosis. The tyrosine phosphatase early gene of liver regeneration (PRL-1), which is involved in the cell cycle, has recently been found to be regulated by halofuginone at a later stage of liver fibrosis (Gnainsky et al 2006). In addition to its known inhibitory effect on collagen α1(I) gene expression (Pines et al 1997a(Pines et al ,b, 2000, halofuginone affects other members of the collagen biosynthesis and degradation pathway, viz., members that are also regulated by TGF-β (Table 1).…”

“…In addition, halofuginone markedly improves the capacity of a cirrhotic liver to regenerate after partial hepatectomy (Spira et al 2002). Recently, we have reported that halofuginone affects the expression of early genes of liver regeneration, namely insulin-like growth-factor-binding protein-1 (IGFBP-1) whose synthesis and secretion is regulated in part by TGF-β (Gnainsky et al 2003) and tyrosine phosphatase (PRL-1) whose synthesis is regulated by transcription factor early growth response-1 (Egr-1) probably via TGF-β (Gnainsky et al 2006). …”

PRL PTPs: mediators and markers of cancer progression

“…At later times post-hepatectomy, PRL-1 upregulation is post-translational, perhaps by RNA stabilization [84]. The plant-derived alkaloid halofuginone, which can inhibit collagen type I synthesis and promote cirrhotic liver regeneration, induces Egr-1 and PRL-1 gene expression in primary rat hepatocytes and hepatocellular carcinoma cell lines [75]. PRL-1 gene expression can also be regulated by the PRL-1 intron enhancer complex (PIEC), a developmentally regulated factor that binds to the first intron of PRL-1 [85].…”

“…PRL-1 expression also leads to increased cyclin A expression that may contribute to enhanced CDK2 activity, but PRL-1 or PRL-2 expression does not alter the expression of cyclin D (G1), cyclin E (G1 to S transition), cyclin B (G2), or the CKI p27 Kip1 (G1). Interestingly, the plant alkaloid halofuginone upregulates PRL-1 expression in several cell lines including HepB3 cells, and in HepB3 cells it also enhances cyclin A level [75].…”