Basic fibroblast growth factor inhibits p38-mediated cell differentiation and growth inhibition by activin A but not by histone deacetylase inhibitors in CML cells

Activin A stimulates the proliferation and differentiation of cardiac fibroblasts via the ERK1/2 and p38-MAPK pathways

Activin A is a key regulator of cardiac fibrosis. However, little is known about the mechanisms by which it contributes to cardiac fibrosis. Our study explored the effects of activin A on proliferation and differentiation of adult rat cardiac fibroblasts (CFs) via the activin A receptor, activin receptor-like kinase 4 (ALK4). CF proliferation was measured by CCK8 and EdU assays, while differentiation, fibrosis and signaling were measured by western blot analysis of α-smooth muscle actin, collagen type I, phosphorylated extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein kinase (p38-MAPK) expression. Activin A levels were measured by ELISA and western blot analysis. We demonstrated that CFs express activin A and its expression was significantly enhanced by angiotensin II (Ang II), but follistatin (activin A inhibitor) significantly reversed Ang II-induced activin A upregulation, CF proliferation, differentiation, collagen type I expression as well as ERK1/2 and p38-MAPK pathways activation. Conversely, recombinant activin A largely increased these parameters in both the presence and absence of Ang II. Interestingly, p38-MAPK (SB203580) and ALK4 (SB431542) inhibitors significantly reduced all activin A-mediated responses; however, an ERK1/2 inhibitor (PD98059) could only significantly reduce CF proliferation and collagen type I expression but not differentiation. Importantly, the most significant effects were observed in the presence vs. absence of Ang II. Thus, activin A promotes basal and Ang II-induced CF proliferation and differentiation via ALK4, and the effects are partly mediated through the ERK1/2 and p38-MAPK pathways. These data suggest that activin A is a potential therapeutic target for cardiac fibrosis.

Activins and Follistatin in Chronic Hepatitis C and Its Treatment with Pegylated-Interferon-α Based Therapy

Pegylated-interferon-α based therapy for the treatment of chronic hepatitis C (CHC) is considered suboptimal as not all patients respond to the treatment and it is associated with several side effects that could lead to dose reduction and/or termination of therapy. The currently used markers to monitor the response to treatment are based on viral kinetics and their performance in the prediction of treatment outcome is moderate and does not combine accuracy and their values have several limitations. Hence, the development of new sensitive and specific predictor markers could provide a useful tool for the clinicians and healthcare providers, especially in the new era of interferon-free therapy, for the classification of patients according to their response to the standard therapy and only subscribing the novel directly acting antiviral drugs to those who are anticipated not to respond to the conventional therapy and/or have absolute contraindications for its use. The importance of activins and follistatin in the regulation of immune system, liver biology, and pathology has recently emerged. This review appraises the up-to-date knowledge regarding the role of activins and follistatin in liver biology and immune system and their role in the pathophysiology of CHC.

Activin A induction of erythroid differentiation sensitizes K562 chronic myeloid leukemia cells to a subtoxic concentration of imatinib

Chronic myeloid leukemia (CML) is a hematopoietic stem/progenitor cell disorder in which Bcr-Abl oncoprotein inhibits cell differentiation. Differentiation induction is considered an alternative strategy for treating CML. Activin A, a member of the transforming growth factor-β superfamily, induces erythroid differentiation of CML cells through the p38 MAPK pathway. In this study, treatment of the K562 CML stem/progenitor cell line with activin A followed by a subtoxic concentration of the Bcr-Abl inhibitor imatinib strongly induced growth inhibition and apoptosis compared with simultaneous treatment with activin A and imatinib. Imatinib-induced growth inhibition and apoptosis following activin A pretreatment were dose- and time-dependent. Imatinib-induced growth inhibition and apoptosis were also dependent on the pretreatment dose of activin A. More than 90% of the activin A-induced increases in glycophorin A-positive cells were sensitive to imatinib. However, only some of original glycophorin A-positive cells in the activin A treatment group were sensitive to imatinib. Sequential treatment with activin A and imatinib decreased Bcr-Abl, procaspase-3, Mcl-1, and Bcl-xL and also induced cleavage of procaspase-3/poly(ADP-ribose)polymerase. The reduction of erythroid differentiation in p38 MAPK dominant-negative mutants or by short hairpin RNA knockdown of p38 MAPK decreased the growth inhibition and apoptosis mediated by sequential treatment with activin A and imatinib. Furthermore, the same inhibition level of multidrug resistance 1 expression was observed in cells treated with activin A alone, treated sequentially with activin A and imatinib, or treated simultaneously with activin A and imatinib. The p38 MAPK inhibitor SB-203580 can restore activin A-inhibited multidrug resistance 1 expression. Taken together, our results suggest that a subtoxic concentration of imatinib could exhibit strong cytotoxicity against erythroid-differentiated K562 CML cells.

Activin A induction of erythroid differentiation through MKK6-p38alpha/p38beta pathway is inhibited by follistatin

Activin A is a member of the transforming growth factor (TGF)-beta superfamily that regulates cell proliferation and differentiation. Using the p38 inhibitor SB203580, our previous studies demonstrated that p38 was involved in activin A-mediated hemoglobin (Hb) synthesis in K562 cells. SB203580 is an inhibitor of p38alpha and p38beta isoforms. In this study, we show that p38alpha and p38beta mRNA were expressed in K562 cells and that activin A activated the kinase activities of these isoforms. To investigate the roles of p38alpha and p38beta isoforms in activin A-mediated erythroid differentiation, we generated stable clones that over-expressed the dominant negative p38 isoforms p38alpha(AF) and p38beta(AF) in K562 cells. The expressions of either p38alpha(AF) or p38beta(AF) reduced activin A-induced p38 activation, Hb synthesis, and zeta-globin promoter activity. Similarly, down-regulation of either p38alpha or p38beta by isoform-specific siRNAs also reduced activin A-induced zeta-globin promoter activity. Co-expressions of p38alpha(AF) and p38beta(AF), together, greatly inhibited the transcription activity of the zeta-globin promoter. Conversely, expression of mitogen-activated protein kinase kinase (MKK) 6b(E), a constitutive activator of p38, significantly activated zeta-globin promoter. Co-expressions of either p38alpha or p38beta with MKK6b had a similar activation of zeta-globin promoter. Activin A induction of erythroid differentiation was inhibited by follistatin. Activin A-induced phosphorylation of MKK6 and p38 was also inhibited by follistatin. Moreover, over-expression of MKK6b(E) reverted follistatin inhibition of activin A-induced zeta-globin promoter activity. These results demonstrate that activin A induces erythroid differentiation of K562 cells through activation of MKK6-p38alpha/p38beta pathway and follistatin inhibits those effects.

p38 Mitogen-activated protein kinase and hematologic malignancies

CONTEXT

p38 mitogen-activated protein kinase (MAPK) signaling has been implicated in responses ranging from apoptosis to cell cycle, induction of expression of cytokine genes, and differentiation. This plethora of activators conveys the complexity of the p38 pathway. This complexity is further complicated by the observation that the downstream effects of p38 MAPK activation may be different depending on types of stimuli, cell types, and various p38 MAPK isoforms involved.

OBJECTIVE

This review focuses on the recent advancement of the p38 MAPK isoforms as well as the roles of p38 MAPK in hematologic malignancies.

DATA SOURCES

Review of pertinent published literature and work in our laboratory.

CONCLUSIONS

In some hematologic malignancies, activation of p38 plays a key role in promoting or inhibiting proliferation and also in increasing resistance to chemotherapeutic agents. The importance of different p38 isoforms in various cellular functions has been acknowledged recently. Further understanding of these isoforms will allow the design of more specific inhibitors to target particular isoforms to maximize the treatment effect and minimize the side effects for treating hematopoietic malignancies.

c-Jun blocks cell differentiation but not growth inhibition or apoptosis of chronic myelogenous leukemia cells induced by STI571 and by histone deacetylase inhibitors

The constitutively active Bcr-Abl tyrosine kinase plays a crucial role in chronic myelogenous leukemia (CML) pathogenesis. The Bcr-Abl protein induces the upregulation of proto-oncogene c-Jun, which is involved in Bcr-Abl transforming activity in Bcr-Abl positive cells. Recent studies reported that c-Jun inhibited hemoglobin synthesis in human CML cell line K562. However, c-Jun also plays a critical role in cell proliferation and apoptosis. In this study, we investigated the physiological roles of c-Jun in cell proliferation, apoptosis and erythroid differentiation of K562 cells. Firstly, we generated K562 cell lines stably overexpressing c-Jun. These clones have the same proliferation rate as the parental cell line in general culture medium. Endogenous c-Jun expression was analyzed to determine the effective concentration of STI571 for inhibiting Bcr-Abl signaling. Western blots show that STI571 inhibited c-Jun expression in a dose-dependent manner, reaching a maximum inhibition at 1 microM. STI571 could inhibit c-Jun expression in K562 cells, but not in c-Jun-overexpression cells. c-Jun did not alter growth inhibition and apoptotic induction by STI571 treatment, but inhibited STI571-induced erythroid differentiation. Moreover, c-Jun did not alter growth inhibition and apoptotic induction by histone deacetylase (HDAC) inhibitors (apicidin, sodium butyrate, and MS275) treatment, but inhibited HDAC inhibitors-induced erythroid differentiation. These results suggest that c-Jun may modulate anticancer drugs-induced cell differentiation but not growth inhibition and apoptosis in CML cells.