Thrombin Mediates Migration of Rat Brain Astrocytes via PLC, Ca2+, CaMKII, PKCα, and AP-1-Dependent Matrix Metalloproteinase-9 Expression

Matrix metalloproteinase-9 (MMP-9) plays a crucial role in pathological processes of brain inflammation, injury, and neurodegeneration. Thrombin has been known as a regulator of MMP-9 expression and cells migration. However, the mechanisms underlying thrombin-induced MMP-9 expression in rat brain astrocytes (RBA-1 cells) remain unclear. Here, we demonstrated that thrombin induced the expression of pro-form MMP-9 and migration of RBA-1 cells, which were inhibited by pretreatment with the inhibitor of Gq-coupled receptor (GPAnt2A), Gi/o-coupled receptor (GPAnt2), PC-PLC (D609), PI-PLC (U73122), Ca²⁺-ATPase (thapsigargin, TG), calmodulin (CaMI), CaMKII (KN62), PKC (Gö6976 or GF109203X), MEK1/2 (PD98059), p38 MAPK (SB202190), JNK1/2 (SP600125), or AP-1 (Tanshinone IIA) or the intracellular calcium chelator (BAPTA/AM) and transfection with siRNA of PKCα, Erk2, JNK1, p38 MAPK, c-Jun, or c-Fos. In addition, thrombin-induced elevation of intracellular Ca²⁺ concentration was attenuated by PPACK (a thrombin inhibitor). Thrombin further induced CaMKII phosphorylation and PKCα translocation, which were inhibited by U73122, D609, KN62, TG, or BAPTA/AM. Thrombin also induced PKCα-dependent p42/p44 MAPK and JNK1/2, but not p38 MAPK activation. Finally, we showed that thrombin enhanced c-Fos expression and c-Jun phosphorylation. c-Fos mRNA levels induced by thrombin were reduced by PD98059, SP600125, and Gö6976, but not SB202190. Thrombin stimulated in vivo binding of c-Fos to the MMP-9 promoter, which was reduced by pretreatment with SP600125 or PD98059, but not SB202190. These results concluded that thrombin activated a PLC/Ca²⁺/CaMKII/PKCα/p42/p44 MAPK and JNK1/2 pathway, which in turn triggered AP-1 activation and ultimately induced MMP-9 expression in RBA-1 cells.     

Doxorubicin Activates Hepatitis B Virus Replication by Elevation of p21 (Waf1/Cip1) and C/EBPα Expression

Hepatitis B virus reactivation is an important medical issue in cancer patients who undergo systemic chemotherapy. Up to half of CHB carriers receiving chemotherapy develop hepatitis and among these cases a notable proportion are associated with HBV reactivation. However, the molecular mechanism(s) through which various chemotherapeutic agents induce HBV reactivation is not yet fully understood. In this study, we investigated the role of the cell cycle regulator p21 (Waf1/Cip1) in the modulation of HBV replication when a common chemotherapeutic agent, doxorubicin, is present. We showed that p21 expression was increased by doxorubicin treatment. This elevation in p21 expression enhanced the expression of CCAAT/enhancer-binding protein α (C/EBPα); such an increase is likely to promote the binding of C/EBPα to the HBV promoter, which will contribute to the activation of HBV replication. Our current study thus reveals the mechanism underlying doxorubicin modulation of HBV replication and provides an increased understanding of HBV reactivation in CHB patients who are receiving systemic chemotherapy.     

Transactivation of Atg4b by C/EBPβ Promotes Autophagy To Facilitate Adipogenesis

Autophagy is a highly conserved self-digestion pathway involved in various physiological and pathophysiological processes. Recent studies have implicated a pivotal role of autophagy in adipocyte differentiation, but the molecular mechanism for its role and how it is regulated during this process are not clear. Here, we show that CCAAT /enhancer-binding protein β (C/EBPβ), an important adipogenic factor, is required for the activation of autophagy during 3T3-L1 adipocyte differentiation. An autophagy-related gene, Atg4b, is identified as a de novo target gene of C/EBPβ and is shown to play an important role in 3T3-L1 adipocyte differentiation. Furthermore, autophagy is required for the degradation of Klf2 and Klf3, two negative regulators of adipocyte differentiation, which is mediated by the adaptor protein p62/SQSTM1. Importantly, the regulation of autophagy by C/EBPβ and the role of autophagy in Klf2/3 degradation and in adipogenesis are further confirmed in mouse models. Our data describe a novel function of C/EBPβ in regulating autophagy and reveal the mechanism of autophagy during adipocyte differentiation. These new insights into the molecular mechanism of adipose tissue development provide a functional pathway with therapeutic potential against obesity and its related metabolic disorders.     

Inhibition of lipogenesis and induction of apoptosis by valproic acid in prostate cancer cells via the C/EBPα/SREBP-1 pathway

Lipid metabolism reprogramming is now accepted as a new hallmark of cancer.Hence,target-ing the lipogenesis pathway may be a potential avenue for cancer treatme...     

The C/EBPβ-Dependent Induction of TFDP2 Facilitates Porcine Reproductive and Respiratory Syndrome Virus Proliferation

Virologica Sinica - Porcine reproductive and respiratory syndrome (PRRS) is an important infectious disease caused by porcine reproductive and respiratory syndrome virus (PRRSV), leading to...     

Protein Inhibitor of Activated STAT 1 (PIAS1) Is Identified as the SUMO E3 Ligase of CCAAT/Enhancer-Binding Protein β (C/EBPβ) during Adipogenesis

It is well recognized that PIAS1, a SUMO (small ubiquitin-like modifier) E3 ligase, modulates such cellular processes as cell proliferation, DNA damage responses, and inflammation responses. Recent studies have shown that PIAS1 also plays a part in cell differentiation. However, the role of PIAS1 in adipocyte differentiation remains unknown. CCAAT/enhancer-binding protein β (C/EBPβ), a major regulator of adipogenesis, is a target of SUMOylation, but the E3 ligase responsible for the SUMOylation of C/EBPβ has not been identified. The present study showed that PIAS1 functions as a SUMO E3 ligase of C/EBPβ to regulate adipogenesis. PIAS1 expression was significantly and transiently induced on day 4 of 3T3-L1 adipocyte differentiation, when C/EBPβ began to decline. PIAS1 was found to interact with C/EBPβ through the SAP (scaffold attachment factor A/B/acinus/PIAS) domain and SUMOylate it, leading to increased ubiquitination and degradation of C/EBPβ. C/EBPβ became more stable when PIAS1 was silenced by RNA interference (RNAi). Moreover, adipogenesis was inhibited by overexpression of wild-type PIAS1 and promoted by knockdown of PIAS1. The mutational study indicated that the catalytic activity of SUMO E3 ligase was required for PIAS1 to restrain adipogenesis. Importantly, the inhibitory effect of PIAS1 overexpression on adipogenesis was rescued by overexpressed C/EBPβ. Thus, PIAS1 could play a dynamic role in adipogenesis by promoting the SUMOylation of C/EBPβ.