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Activation of STAT3 by the hepatitis C virus core protein leads to cellular transformation.

Yoshida T, Hanada T, Tokuhisa T, Kosai K, Sata M, Kohara M, Yoshimura A - J. Exp. Med. (2002)

Bottom Line: Activation of STAT3 by the HCV core in NIH-3T3 cells resulted in rapid proliferation and up-regulation of Bcl-XL and cyclin-D1.Additional expression of STAT3 in HCV core-expressing cells resulted in anchorage-independent growth and tumorigenesis.We propose that the HCV core protein cooperates with STAT3, which leads to cellular transformation.

View Article: PubMed Central - PubMed

Affiliation: Division of Molecular and Cellular Immunology, Medical Institute of Bioregulation, Kyushu University, Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.

ABSTRACT
The signal transducer and activator of transcription (STAT) family proteins are transcription factors critical in mediating cytokine signaling. Among them, STAT3 is often constitutively phosphorylated and activated in human cancers and in transformed cell lines and is implicated in tumorigenesis. However, cause of the persistent activation of STAT3 in human tumor cells is largely unknown. The hepatitis C virus (HCV) is a major etiological agent of non-A and non-B hepatitis, and chronic infection by HCV is associated with development of liver cirrhosis and hepatocellular carcinoma. HCV core protein is proposed to be responsible for the virus-induced transformation. We now report that HCV core protein directly interacts with and activates STAT3 through phosphorylation of the critical tyrosine residue. Activation of STAT3 by the HCV core in NIH-3T3 cells resulted in rapid proliferation and up-regulation of Bcl-XL and cyclin-D1. Additional expression of STAT3 in HCV core-expressing cells resulted in anchorage-independent growth and tumorigenesis. We propose that the HCV core protein cooperates with STAT3, which leads to cellular transformation.

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Related in: MedlinePlus

Cell extracts were prepared from parental NIH-3T3 cells (parent; lane 1), core-infected cells (core) (lane 2), and representative clones isolated from soft agar (STAT3 + core [lane 4], STAT3-C [lane 5], and v-src [lane 6]), and NIH-3T3 transformant expressing WT-STAT3 (lane 3), then immunoblotted with the indicated antibodies.
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fig8: Cell extracts were prepared from parental NIH-3T3 cells (parent; lane 1), core-infected cells (core) (lane 2), and representative clones isolated from soft agar (STAT3 + core [lane 4], STAT3-C [lane 5], and v-src [lane 6]), and NIH-3T3 transformant expressing WT-STAT3 (lane 3), then immunoblotted with the indicated antibodies.

Mentions: Next, we examined effects of core protein on cellular transformation. Recent studies suggested that STAT3 is necessary for the full transforming activity of v-src and that a constitutively activated form of STAT3 (STAT3-C) transformed normal fibroblasts (5–7). Thus, we examined the transforming potential of the core protein in combination with wild-type (WT)-STAT3 or STAT3-C. As shown in Table I and Fig. 6 A, expression of only the core (pMX-core) or transfection of the WT-STAT3 did not produce colonies in soft agar. However, transfection of WT-STAT3 into NIH-3T3 cells infected with the pMX-core did result in colony formation. The efficiency of colony formation and colony size by WT-STAT3 and the core (WT-STAT3/core) were comparable to those seen with STAT3-C (Fig. 6 A and Table I). The combination of the core and STAT3-C further increased colony formation efficiency (Table I). Cells were recovered from these transformed colonies and cultured. The levels of exogenous WT-STAT3 in these cells formed in soft agar were 1.5–2 times higher than endogenous STAT3 (Fig. 6 B), and both exogenous and endogenous STAT3 were tyrosine phosphorylated by the core (see Fig. 8) . Therefore, the level of STAT3 is critical for transformation by the core protein. Requirement of further STAT3 expression for transformation in NIH-3T3 cells may be due to relatively low contents of STAT3 in this fibroblastic cell line compared with contents in the hepatocarcinoma cell line HepG2 and mouse liver tissues (Fig. 6 B, and unpublished data).


Activation of STAT3 by the hepatitis C virus core protein leads to cellular transformation.

Yoshida T, Hanada T, Tokuhisa T, Kosai K, Sata M, Kohara M, Yoshimura A - J. Exp. Med. (2002)

Cell extracts were prepared from parental NIH-3T3 cells (parent; lane 1), core-infected cells (core) (lane 2), and representative clones isolated from soft agar (STAT3 + core [lane 4], STAT3-C [lane 5], and v-src [lane 6]), and NIH-3T3 transformant expressing WT-STAT3 (lane 3), then immunoblotted with the indicated antibodies.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2194001&req=5

fig8: Cell extracts were prepared from parental NIH-3T3 cells (parent; lane 1), core-infected cells (core) (lane 2), and representative clones isolated from soft agar (STAT3 + core [lane 4], STAT3-C [lane 5], and v-src [lane 6]), and NIH-3T3 transformant expressing WT-STAT3 (lane 3), then immunoblotted with the indicated antibodies.
Mentions: Next, we examined effects of core protein on cellular transformation. Recent studies suggested that STAT3 is necessary for the full transforming activity of v-src and that a constitutively activated form of STAT3 (STAT3-C) transformed normal fibroblasts (5–7). Thus, we examined the transforming potential of the core protein in combination with wild-type (WT)-STAT3 or STAT3-C. As shown in Table I and Fig. 6 A, expression of only the core (pMX-core) or transfection of the WT-STAT3 did not produce colonies in soft agar. However, transfection of WT-STAT3 into NIH-3T3 cells infected with the pMX-core did result in colony formation. The efficiency of colony formation and colony size by WT-STAT3 and the core (WT-STAT3/core) were comparable to those seen with STAT3-C (Fig. 6 A and Table I). The combination of the core and STAT3-C further increased colony formation efficiency (Table I). Cells were recovered from these transformed colonies and cultured. The levels of exogenous WT-STAT3 in these cells formed in soft agar were 1.5–2 times higher than endogenous STAT3 (Fig. 6 B), and both exogenous and endogenous STAT3 were tyrosine phosphorylated by the core (see Fig. 8) . Therefore, the level of STAT3 is critical for transformation by the core protein. Requirement of further STAT3 expression for transformation in NIH-3T3 cells may be due to relatively low contents of STAT3 in this fibroblastic cell line compared with contents in the hepatocarcinoma cell line HepG2 and mouse liver tissues (Fig. 6 B, and unpublished data).

Bottom Line: Activation of STAT3 by the HCV core in NIH-3T3 cells resulted in rapid proliferation and up-regulation of Bcl-XL and cyclin-D1.Additional expression of STAT3 in HCV core-expressing cells resulted in anchorage-independent growth and tumorigenesis.We propose that the HCV core protein cooperates with STAT3, which leads to cellular transformation.

View Article: PubMed Central - PubMed

Affiliation: Division of Molecular and Cellular Immunology, Medical Institute of Bioregulation, Kyushu University, Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.

ABSTRACT
The signal transducer and activator of transcription (STAT) family proteins are transcription factors critical in mediating cytokine signaling. Among them, STAT3 is often constitutively phosphorylated and activated in human cancers and in transformed cell lines and is implicated in tumorigenesis. However, cause of the persistent activation of STAT3 in human tumor cells is largely unknown. The hepatitis C virus (HCV) is a major etiological agent of non-A and non-B hepatitis, and chronic infection by HCV is associated with development of liver cirrhosis and hepatocellular carcinoma. HCV core protein is proposed to be responsible for the virus-induced transformation. We now report that HCV core protein directly interacts with and activates STAT3 through phosphorylation of the critical tyrosine residue. Activation of STAT3 by the HCV core in NIH-3T3 cells resulted in rapid proliferation and up-regulation of Bcl-XL and cyclin-D1. Additional expression of STAT3 in HCV core-expressing cells resulted in anchorage-independent growth and tumorigenesis. We propose that the HCV core protein cooperates with STAT3, which leads to cellular transformation.

Show MeSH
Related in: MedlinePlus