Jörg Schrader

UNLABELLED: There is increasing evidence that the physical environment is a critical mediator of tumor behavior. Hepatocellular carcinoma (HCC) develops within an altered biomechanical environment, and increasing matrix stiffness is a strong predictor of HCC development. The aim of this study was to establish whether changes in matrix stiffness, which are characteristic of inflammation and fibrosis, regulate HCC cell proliferation and chemotherapeutic response. Using an in vitro system of "mechanically tunable" matrix-coated polyacrylamide gels, matrix stiffness was modeled across a pathophysiologically relevant range, corresponding to values encountered in normal and fibrotic livers. Increasing matrix stiffness was found to promote HCC cell proliferation. The proliferative index (assessed by Ki67 staining) of Huh7 and HepG2 cells was 2.7-fold and 12.2-fold higher, respectively, when the cells were cultured on stiff (12 kPa) versus soft (1 kPa) supports. This was associated with stiffness-dependent regulation of basal and hepatocyte growth factor-stimulated mitogenic signaling through extracellular signal-regulated kinase, protein kinase B (PKB/Akt), and signal transducer and activator of transcription 3. β1-Integrin and focal adhesion kinase were found to modulate stiffness-dependent HCC cell proliferation. Following treatment with cisplatin, we observed reduced apoptosis in HCC cells cultured on stiff versus soft (physiological) supports. Interestingly, however, surviving cells from soft supports had significantly higher clonogenic capacity than surviving cells from a stiff microenvironment. This was associated with enhanced expression of cancer stem cell markers, including clusters of differentiation 44 (CD44), CD133, c-kit, cysteine-X-cysteine receptor 4, octamer-4 (CXCR4), and NANOG. CONCLUSION: Increasing matrix stiffness promotes proliferation and chemotherapeutic resistance, whereas a soft environment induces reversible cellular dormancy and stem cell characteristics in HCC. This has implications for both the treatment of primary HCC and the prevention of tumor outgrowth from disseminated tumor cells. (HEPATOLOGY 2011;).

TGF-beta induces the conversion of CD4(+)CD25(-) T cells into CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg). Activin A is a pleiotropic TGF-beta family member and is expressed in response to inflammatory signals. In this study, we report on the effects of activin A on the conversion of CD4(+)CD25(-) T cells into Foxp3-expressing induced Treg (iTreg). Activin A was able to promote the conversion of CD4(+)CD25(-) T cells into iTreg in a dose-dependent manner in vitro. Activin A together with TGF-beta1 had synergistic effects on the rate of iTreg conversion in vitro. Intact TGF-beta1 signaling seemed to be essential for the effects of activin A on iTreg generation because cells overexpressing a dominant negative TGF-beta type II receptor could not be converted by activin A in vitro. In vivo, the frequency of peripheral, but not central, Treg was increased in transgenic mice with elevated activin A serum levels and the in vivo conversion rate of CD4(+)CD25(-) T cells into Foxp3-expressing iTreg was increased as compared with wild type mice. These data suggest a role for activin A as a promoter of the TGF-beta dependent conversion of CD4(+)CD25(-) T cells into iTreg in vitro and in vivo. Therefore, besides promoting inflammation, activin A may contribute to the regulation of inflammation via the expansion of peripheral Treg.