Signal transduction mechanisms involved in S100A4-induced activation of the transcription factor NF-kappaB

BACKGROUND

The metastasis-promoting protein S100A4 activates the transcription factor NF-kappaB through the classical NF-kappaB activation pathway. The upstream signal transduction mechanisms leading to increased NF-kappaB activity are, however, incompletely characterized.

METHODS

The human osteosarcoma cell line II-11b was stimulated with recombinant S100A4 in the presence or absence of inhibitors of common signal transduction pathways, and NF-kappaB activity was examined using a luciferase-based reporter assay and phosphorylation of IkappaBalpha. mRNA expression was analyzed by real-time RT-PCR, protein expression was examined by Western blotting and IKK activity was measured using an in vitro kinase assay. The role of upstream kinases and the cell surface receptor RAGE was investigated by overexpression of dominant negative proteins and by siRNA transfection.

RESULTS

The Ser/Thr kinase inhibitors H-7 and staurosporine inhibited S100A4-induced IkappaBalpha phosphorylation and subsequent NF-kappaB activation. The protein tyrosine kinase inhibitor genistein and the phospholipase C inhibitor compound 48/80 had a partial inhibitory effect on IkappaBalpha phosphorylation, whereas inhibitors of protein kinase C, G-protein coupled receptors and PI 3-kinases had no effect on the level of phosphorylation. Interestingly, S100A4 treatment induced activating phosphorylations of IKKalpha/beta, but neither H-7 nor staurosporine was able to significantly inhibit IKK activation. Dominant negative MEKK1 or NIK did not inhibit S100A4-induced NF-kappaB activity, and S100A4 stimulation did not influence AKT phosphorylation. Furthermore, diminished expression of the putative S100 protein receptor RAGE did not affect the observed phosphorylation of IkappaBalpha.

CONCLUSIONS

S100A4 activates NF-kappaB by inducing phosphorylation of IKKalpha/beta, leading to increased IkappaBalpha phosphorylation. The Ser/Thr kinase inhibitors H-7 and staurosporine attenuated S100A4-induced NF-kappaB activation and inhibited IKK-mediated phosphorylation of IkappaBalpha. S100A4-induced NF-kappaB activation was independent of the putative S100 protein receptor RAGE and the Ser/Thr kinases MEKK1, NIK and AKT. These findings lead to increased understanding of S100A4 signaling, which may contribute to the identification of novel targets for anti-metastatic therapy.

Abstract 4304: Malignant melanoma cells with aggressive properties are common and not distinguishable by proposed markers for cancer stem cells

In malignant melanoma, conflicting results have been reported regarding the presence of exclusive cells with enhanced aggressive properties, so called cancer stem cells (CSC), raising a doubt whether melanoma follows a CSC model and is hierarchically organized. By characterizing melanoma cells from short-term cell cultures, xenografts and patient biopsies, we aim to collect further evidence either to: i) support the existence of distinct CSC-like subpopulations, or ii) strengthen a notion about the common presence of cells demonstrating aggressive behavior and lack of cellular hierarchy in melanoma. By using individual-cell assays, we have shown that a large fraction (up to 60 %) of random single melanoma cells display high clonogenicity and self-renewal i.e. properties associated with tumorigenic potential. In search for a marker for such clonogenic/tumorigenic cells, we found that melanomas often harbor a large distinct subpopulation with elevated activity of Aldehyde Dehydrogenase (ALDH), a proposed marker for CSC-like cells in some hierarchically organized cancers. Interestingly, ALDH activity in melanoma patient biopsies seemed to correlate to the expression of melanoma-associated-antigen, HMW-MAA, which is linked to tumor progression. Furthermore, in vivo ALDH+ melanoma cells could convert to ALDH−, while the opposite conversion was rare, indicating a certain “cellular hierarchy” with respect to the ALDH phenotype. However, comparison of ALDH+ and ALDH− cells revealed that both subpopulations are highly clonogenic, tumorigenic and resistant to drugs proposed for melanoma therapy, DTIC and HGS-ETR2. This suggests that in malignant melanoma, ALDH, likewise earlier investigated “surface markers” of CSCs, does not distinguish cells with enhanced biological aggressiveness. In conclusion, melanoma cells exhibiting properties linked to aggressive phenotype are common and not restricted to subpopulations expressing proposed “CSC markers”, which contradicts the traditional view of CSCs.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4304.

Abstract LB-73: Nuclear S100A4 is a novel prognostic marker in colorectal cancer

Background and Aims: Current staging classifications in colorectal cancer are not able to accurately predict patient outcome, and the need for novel prognostic markers is evident. S100A4 is a Ca2+-binding protein which promotes metastasis in several tumor types, and the aim of the present study was to investigate the prognostic impact of S100A4 expression in colorectal cancer.

Methods:

242 patients with curatively resected adenocarcinoma of the colon or rectum were prospectively included in the study at the time of surgery. S100A4 expression was analyzed by immunohistochemistry, and associations with clinicopathological variables and patient outcome were investigated.

Results: Nuclear expression of S100A4 was observed in 29% and cytoplasmic expression was observed in 64% of the tumors. In univariate analysis, nuclear S100A4 was a significant predictor of metastasis-free (P= .006) and overall survival (P= .01), whereas cytoplasmic S100A4 was not associated with patient outcome. In multivariate analysis, nuclear localization was associated with metastasis-free (P= .03) and overall survival (P= .02). Interestingly, the prognostic impact was largely confined to TNM stage II, and stage II patients with tumors expressing nuclear S100A4 had a similar prognosis as stage III patients.

Conclusions: Nuclear expression of S100A4 is a novel prognostic marker in colorectal cancer, and the prognostic value in TNM stage II suggests that nuclear S100A4 could be used in the stratification of stage II patients for adjuvant treatment.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-73.

Abstract 2550: B7-H3 induces paclitaxel resistance in human breast cancer cell lines

B7-H3 is previously known as an immunoregulatory protein with either stimulatory or inhibitory effects on the activation of T-cells. The correlation between high expression of B7-H3 and poor prognosis has been reported in many human tumor types and this has been ascribed to the putative immune-regulatory function of the protein. Previously, we reported results indicating a direct association between B7-H3 expression and metastasis, whereas in this study we examined the role of B7-H3 with respect to paclitaxel resistance in metastatic breast cancer cells as well as the underlying mechanisms. The results show that silencing B7-H3 increased the sensitivity to both MDA-MB-231 and MDA-MB-435 breast cancer cells to paclitaxel. This drug is known to exert its cell killing effect through induction of apoptosis, and our data confirmed that the silencing of B7-H3 sensitized breast cancer cells to paclitaxel-induced apoptosis. The extent of apoptosis was investigated by checking the amount of Annexin-5 stained cells, a marker for early stage apoptosis and for the amount of TUNEL positive cells, which reflects late stage apoptosis. To confirm the apoptotic response observed by the use of flow cytometry, we examined the cleavage of poly (ADP-ribose) polymerase (PARP), another marker of apoptosis, and found that MDA-MB-231 and MDA-MB-435 B7-H3 knockdown cells showed increased PARP cleavage compared to the vector control cells upon treatment with paclitaxel.

We then studied whether the effects of B7-H3 on drug resistance could be related to molecules and signaling pathways known to be involved in the apoptotic response. Interestingly we discovered that the STAT3 pathway, also known to be involved in chemo-resistance, was affected by B7-H3, with markedly decreased phosphorylation of STAT3 Tyr705 in B7-H3 knockdown cells. Furthermore, two members of the IAP family of antiapoptotic proteins, survivin and Mcl-1 which are direct downstream targets of Stat3, were both repressed by the decrease in B7-H3 and Stat3 phosphorylation levels.

The phosphorylation level of JAK2, which is a well-known upstream component of STAT3 signaling, was also significantly decreased in B7-H3 knockdown cells.

Finally, in vivo experiments showed that in nude mice treated with paclitaxel, the growth rate of tumors in the mice injected s.c with MDA-MB-435 B7-H3 knockdown cells was significantly reduced in contrast to the growth rate in mice injected with MDA-MB-435 control cells. Taken together, our data demonstrates that in breast cancer cells B7-H3 expression is associated with antiapoptosis and paclitaxel resistance, at least partly through the STAT3 pathway

The novel findings of this study have important implications for the design of new approaches targeting B7-H3 overexpressing breast cancers.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2550.

Coexpression and nuclear colocalization of metastasis-promoting protein S100A4 and p53 without mutual regulation in colorectal carcinoma

Nuclear localization of the metastasis-associated protein S100A4 has been shown to correlate with advanced disease stage in primary colorectal carcinomas (CRC), but nuclear function and its relevance for the metastatic capacity of tumor cells is still unclear. Among several nuclear interacting protein partners suggested for S100A4, the tumor suppressor protein p53 has attracted particular interest, and previous studies suggest direct and indirect modes of interaction between the two proteins. The present study was undertaken to assess coexpression and potential interaction in CRC. TP53 mutational status and S100A4 expression were investigated in a selected series of primary CRC specimens (n = 40) and cell lines (n = 17) using DNA sequencing, western blot, and double immunostaining. Additionally, S100A4 and p53 were experimentally up- and down-regulated in vitro to assess reciprocal effects. For the first time, S100A4 and p53 coexpression was demonstrated in individual CRC cells, with nuclear colocalization as a particularly interesting feature. In contrast to previous studies, no correlation was observed between TP53 mutational status and S100A4 expression, and no evidence was obtained to support reciprocal regulation between the two molecules in the HCT116 isogenic cell line model. In conclusion, S100A4 and p53 were shown to be colocalized in individual nuclei of CRC cells, and it might be speculated whether the proteins interact in this subcellular compartment.

Interferon-gamma suppresses S100A4 transcription independently of apoptosis or cell cycle arrest

The S100A4 protein has been associated with increased metastatic capacity of cancer cells, and recent studies have suggested a correlation between the expression level of S100A4 and the prognostic outcome for patients with various types of cancer. The knowledge about the mechanisms underlying the metastasis-promoting effects is still limited, and the aim of the present study was to elucidate signal transduction pathways involved in the regulation of S100A4. After treatment of human carcinoma cells with interferon-gamma (IFN-gamma), we observed downregulation of S100A4 both at mRNA and protein levels. The effect was not dependent on IFN-gamma-induced apoptosis or IFN-gamma-mediated cell cycle arrest. Moreover, IFN-gamma-mediated decrease in mRNA stability could not account for the observed decrease in S100A4 transcript level. Finally, microarray analysis suggests ISGF3G, ETV5, ZNF133 and CEBPG as possible candidate genes involved in IFN-gamma-mediated repression of S100A4.