ARP3 promotes tumor metastasis and predicts a poor prognosis in hepatocellular carcinoma.

Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related death worldwide. Therefore, the study of the precise molecular mechanism underlying hepatocarcinogenesis has profound significance. In this study, we found that the expression of ARP3 was significantly up-regulated in HCC tissues and cell lines. Studies in liver cancer specimens showed that the expression of ARP3 is closely related to the pathological grade, distant metastasis and vascular invasion of HCC. According to the results of multivariate analysis, ARP3 is an independent prognostic factor for HCC patients. In vitro, knockdown of ARP3 expression significantly inhibited the invasion and migration of HCC cells and altered the expression of EMT markers. Based on the above conclusions, we conclude that ARP3 may be a potential prognostic indicator and therapeutic target for HCC patients.

Nuclear actin filaments recruit cofilin and actin-related protein 3, and their formation is connected with a mitotic block.

Although actin monomers polymerize into filaments in the cytoplasm, the form of actin in the nucleus remains elusive. We searched for the form and function of ß-actin fused to nuclear localization signal and to enhanced yellow fluorescent protein (EN-actin). Our results reveal that EN-actin is either dispersed in the nucleoplasm (homogenous EN-actin) or forms bundled filaments in the nucleus (EN-actin filaments). Formation of such filaments was not connected with increased EN-actin levels. Among numerous actin-binding proteins tested, only cofilin is recruited to the EN-actin filaments. Overexpression of EN-actin causes increase in the nuclear levels of actin-related protein 3 (Arp3). Although Arp3, a member of actin nucleation complex Arp2/3, is responsible for EN-actin filament nucleation and bundling, the way cofilin affects nuclear EN-actin filaments dynamics is not clear. While cells with homogenous EN-actin maintained unaffected mitosis during which EN-actin re-localizes to the plasma membrane, generation of nuclear EN-actin filaments severely decreases cell proliferation and interferes with mitotic progress. The introduction of EN-actin manifests in two mitotic-inborn defects-formation of binucleic cells and generation of micronuclei-suggesting that cells suffer aberrant cytokinesis and/or impaired chromosomal segregation. In interphase, nuclear EN-actin filaments passed through chromatin region, but do not co-localize with either chromatin remodeling complexes or RNA polymerases I and II. Surprisingly presence of EN-actin filaments was connected with increase in the overall transcription levels in the S-phase by yet unknown mechanism. Taken together, EN-actin can form filaments in the nucleus which affect important cellular processes such as transcription and mitosis.

[Association of intracellular proteinase activities with the content of locomotor proteins in tissues of primary tumors and metastasis in ovarian cancer].

The ability to active movement in extracellular matrix wherein significant role plays remodeling of the cytoskeleton by actin-binding proteins may influence on the metastatic potential of tumor cells. We studied the expression of actin-binding proteins and ß-catenin in connection with proteasome and calpain functioning in the tissues of primary tumors and metastases of ovarian cancer. The chymotrypsin-like proteasome activity and calpain activity were shown to be significantly higher in ovarian cancer than in normal tissues. Furthermore, the activity of the proteasome and calpain were significantly higher in the peritoneal metastases in comparison with primary tumors. Correlation analysis showed in the primary tumor tissue the presence of a positive relationship between the activity of calpain and chymotrypsin-like proteasome activity (r = 0.82; p = 0.0005), whereas in metastases this connection was not revealed. Contents of p45 Ser ß-catenin and the actin-severing protein gelzolin were decreased in metastases relative to primary tumors. Level of cofilin, functionally similar to gelzolin protein, was significantly higher in metastases compared to primary ovarian tumor tissue. In ovarian cancer significant reduction in the number of the monomer binder protein thymosin-ß4 was observed in primary tumors and metastases as compared to normal tissues, but significant differences between the primary tumor and metastases were not observed. In the tissues of primary tumors negative correlations were observed between the chymotrypsin-like activity of the proteasome and the amount of p45 Ser ß-catenin and protein Arp3, a member of the Arp2/3 complex. In metastasis negative correlation were revealed between the activity of calpain and content Arp3, cofilin, thymosin. The data obtained suggest the existence of different mechanisms of proteolytic regulation of locomotor proteins in primary tumors and metastases in ovarian cancer.

Arp2/3 overexpression contributed to pathogenesis, growth and invasion of gastric carcinoma.

BACKGROUND: Tumor metastasis depends on cell adhesion, motility and deformability, resulting from quantitative alterations and rearrangement of actin-related protein (Arp) 2 and 3. The aim of this study was to clarify the roles of both molecules in tumorigenesis and progression of gastric carcinomas. PATIENTS AND METHODS: Immunohistochemistry (IHC) was employed on tissue microarray containing gastric carcinomas, adjacent metaplasia and gastritis using antibodies against Arp2 and Arp3 with a comparison of their expression with clinicopathological parameters of carcinomas. Gastric carcinoma cell lines (MKN28, AGS, MKN45, KATO-III and HGC-27) were studied for Arp2 and Arp3 protein by IHC. RESULTS: Both proteins were expressed at low levels in gastritis compared with carcinomas (p < 0.05). Arp2 was more frequently expressed in intestinal metaplasia than in carcinoma and gastritis (p < 0.05). Most gastric carcinoma cell lines showed expression at different levels. Expression was positively correlated with tumor size, depth of invasion, venous invasion, Union Internationale Contre le Cancer (UICC) staging and expression of cortactin or fascin (p < 0.05), but not with age, sex, lymphatic invasion or lymph node metastasis (p > 0.05). There was stronger positivity of Arp3 in intestinal- than diffuse-type carcinomas (p < 0.05). A positive relationship between Arp2 and Arp3 proteins was noted (p < 0.05). Univariate analysis indicated that the cumulative survival rate of patients with positive Arp2 or Arp3 expression was not different from those without their expression (p > 0.05). Multivariate analysis showed that age, depth of invasion, lymphatic invasion, lymph node metastasis, UICC staging and Lauren's classification were independent prognostic factors for carcinomas (p < 0.05). CONCLUSION: Aberrant expression of Arp2 and Arp3 is possibly involved in pathogenesis, growth, invasion and progression of gastric carcinomas. Distinct Arp3 expression underlies the molecular mechanisms for the differentiation of intestinal- and diffuse-type carcinomas. They were considered as objective and effective markers to indicate the pathobiological behaviors of gastric carcinomas.