Diverse mechanisms of Wnt activation and effects of pathway inhibition on proliferation of human gastric carcinoma cells

Abstract

Human gastric carcinomas are among the most treatment refractory epithelial malignancies. Increased understanding of the underlying molecular aberrations in such tumors could provide insights leading to improved therapeutic approaches. In this study, we characterized diverse genetic aberrations leading to constitutive Wnt signaling activation in a series of human gastric carcinoma cell lines. Downregulation of TCF signaling by stable transduction of dominant negative TCF-4 (DNTCF4) resulted in inhibition of proliferation in Wnt activated AGS tumor cells. c-Myc downregulation and the associated upregulation of its repression target, p21 observed in these tumor cells, as well as the profound growth inhibition induced by c-Myc shRNA implied their c-Myc addiction. In striking contrast, Wnt activated MKN-28 and MKN-74 tumor cells appeared refractory to DNTCF4 inhibition of proliferation despite comparably decreased c-Myc expression levels. The resistance of these same tumor cells to growth inhibition by c-Myc shRNA established that their refractoriness to DNTCF was due to their independence from c-Myc for proliferation. There was no correlation between this resistance phenotype and the presence or absence of constitutive MAPK and/or AKT pathway activation, commonly observed in gastrointestinal tumors. However, in both DNTCF sensitive and resistant tumor cells with MAPK and/or AKT pathway activation, the ability of small molecule antagonists directed against either pathway to inhibit tumor cell growth was enhanced by Wnt pathway inhibition. These findings support the concept that while certain Wnt activated tumors may escape c-Myc dependence for proliferation, disruption of other oncogenic pathways can unmask cooperative antiproliferative effects for Wnt pathway downregulation.

High-resolution chromatin immunoprecipitation (ChIP) sequencing reveals novel binding targets and prognostic role for SOX11 in mantle cell lymphoma

“…We further confirmed that direct inhibition of WNT pathway down-stream effector TCF/LEF activity via a dominant negative TCF4 (Dn-TCF4) construct (23) can recapitulate the functional phenotypes of proliferation repression and G2/M arrest induced by SOX11 forced expression. Using Granta-519 (Figure 4D, 4E) and Z138 (Supplementary Figure S5A, S5B) cell lines, we showed that DN-TCF4 transfected cells (orange) exhibited significant proliferative arrest (Figure 4D, Supplementary Figure S5A) compared to control plasmid transfected cells (green).…”

“…SMAD3 reporter construct (SMAD3p-Luc) containing SOX11 consensus sequence was kindly gifted by Dr. Thomas J. Kelly (49). DN-TCF4 was a kind gift by Dr. Stuart A. Aaronson (23) and was subsequently cloned into an expression vector containing IRES-eGFP (Ex-M60) for overexpression experiment. SOX11 siRNA sequences were listed in supplementary table 8.…”

Wnt3a Reestablishes Osteogenic Capacity to Bone Grafts from Aged Animals

“…Although exogenously applied Wnt3a has great potential as a therapeutic protein, safety remains a primary concern. The delivery of high concentrations of potent growth factors to a skeletal injury site carries with it potential oncological risk to the patient 50 . To circumvent issues associated with prolonged or uncontrolled exposure to a growth factor, we delivered L-Wnt3a ex vivo.…”

Chibby is a weak regulator of β‐catenin activity in gastric epithelium

“…The AGS cell line was derived from human gastric adenocarcinoma. The β‐catenin gene in AGS cells contains an activating mutation that results in the unregulated proliferation of the cells (Asciutti, Akiri, Grumolato, Vijayakumar, & Aaronson, ). Because Cby functions as a β‐catenin antagonist, we examined the effect of Cby overexpression on β‐catenin levels and cell growth in AGS cells.…”