Tenascin-C (TN-C) is an extracellular matrix molecule that is expressed during wound healing in various tissues. Although not detectable in the normal adult heart, it is expressed under pathological conditions. Previously, using a rat model, we found that TN-C was expressed during the acute stage after myocardial infarction and that alpha-smooth muscle actin (alpha-SMA)-positive myofibroblasts appeared in TN-C-positive areas. In the present study, we examined whether TN-C controls the dynamics of myofibroblast recruitment and wound healing after electrical injury to the myocardium of TN-C knockout (TNKO) mice compared with wild-type (WT) mice. In TNKO mice, myocardial repair seemed to proceed normally, but the appearance of myofibroblasts was delayed. With cultured cardiac fibroblasts, TN-C significantly accelerated cell migration, alpha-SMA expression, and collagen gel contraction but did not affect proliferation. Using recombinant fragments of murine TN-C, the functional domain responsible for promoting migration of cardiac fibroblasts was mapped to the conserved fibronectin type III (FNIII)-like repeats and the fibrinogen (Fbg)-like domain. Furthermore, alternatively spliced FNIII and Fbg-like domains proved responsible for the up-regulation of alpha-SMA expression. These results indicate that TN-C promotes recruitment of myofibroblasts in the early stages of myocardial repair by stimulating cell migration and differentiation.

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Degree of histological differentiation is an important characteristic of cancers and may be associated with malignant potential. However, in squamous cell carcinomas, a key transcriptional factor regulating tumor differentiation is largely unknown. Chemoradiotherapy (CRT) is a standard treatment for locally advanced esophageal squamous cell carcinoma; however, the survival rate is still below 40%. From microarray data, single‐minded 2 (SIM2) was overexpressed in the epithelial subtype. Here, we investigated the correlation between SIM2 expression and its clinical implication, and in vitro and in vivo functions of SIM2 in tumor differentiation and in CRT sensitivity. Although SIM2 was suppressed in cancerous tissues, SIM2‐high ESCC showed a favorable prognosis in CRT. Transient SIM2 expression followed by 3D culture induced expression of differentiation markers and suppressed epithelial‐mesenchymal transition‐ and basal‐cell markers. Levels of PDPN‐high tumor basal cells and of expression of genes for DNA repair and antioxidant enzymes were reduced in stable transfectants, and they showed high CDDP and H2O2 sensitivities, and their xenografts showed a well‐differentiated histology. Reduction of tumor basal cells was restored by knockdown of aryl hydrocarbon receptor nuclear translocator (ARNT) that interacted with SIM2. Together, SIM2 increases CRT sensitivity through tumor differentiation by cooperation with ARNT.

Diffuse-type solid tumors are often composed of a high proportion of rarely proliferating (i.e., dormant) cancer cells, strongly indicating the involvement of cancer stem cells (CSCs) Although diffuse-type gastric cancer (GC) patients have a poor prognosis due to high-frequent development of peritoneal dissemination (PD), it is limited knowledge that the PD-associated CSCs and efficacy of CSC-targeting therapy in diffuse-type GC. In this study, we established highly metastatic GC cell lines by in vivo selection designed for the enrichment of PD-associated GC cells. By microarray analysis, we found C-X-C chemokine receptor type 4 (CXCR4) can be a novel marker for highly metastatic CSCs, since CXCR4-positive cells can grow anchorage-independently, initiate tumors in mice, be resistant to cytotoxic drug, and produce differentiated daughter cells. In clinical samples, these CXCR4-positive cells were found from not only late metastasis stage (accumulated ascites) but also earlier stage (peritoneal washings). Moreover, treatment with transforming growth factor-β enhanced the anti-cancer effect of docetaxel via induction of cell differentiation/asymmetric cell division of the CXCR4-positive gastric CSCs even in a dormant state. Therefore, differentiation inducers hold promise for obtaining the maximum therapeutic outcome from currently available anti-cancer drugs through re-cycling of CSCs.

Esophageal squamous cell carcinoma (ESCC) is one of the most common malignant tumors. Although improvement in both surgical techniques and neoadjuvant chemotherapy has been achieved, the 5‐year survival rate of locally advanced tumors was, at best, still 55%. Therefore, elucidation of mechanisms of the malignancy is eagerly awaited. Epithelial‐mesenchymal transition (EMT) by transforming growth factor‐β (TGF‐β) has been reported to have critical biological roles for cancer cell stemness, whereas little is known about it in ESCC. In the current study, a transcriptional factor SIX1 was found to be aberrantly expressed in ESCCs. SIX1 cDNA transfection induced overexpression of transforming growth factors (TGFB1 and TGFB2) and its receptor (TGFBR2). Cell invasion was reduced by SIX1 knockdown and was increased in stable SIX1‐transfectants. Furthermore, the SIX1‐transfectants highly expressed tumor basal cell markers such as NGFR,SOX2,ALDH1A1, and PDPN. Although mock‐transfectants had only a 20% PDPN‐high population, SIX1‐transfectants had 60–70%. In two sets of 42 and 85 ESCC patients receiving surgery alone or neoadjuvant chemoradiotherapy followed by surgery, the cases with high SIX1 mRNA and protein expression level significantly showed a poor prognosis compared with those with low levels. These SIX1 high cases also expressed the above basal cell markers, but suppressed the differentiation markers. Finally, TGF‐β signaling blockade suppressed ESCC cell growth in association with the reduction of PDPN‐positive tumor basal cell population. The present results suggest that SIX1 accelerates self‐renewal of tumor basal cells, resulting in a poor prognosis for ESCC patients.