A function for Stat3β in embryonic stem cell self-renewal

• Main Author: Stracey, Craig
• Published: University of Edinburgh 2001
• Subjects: 611
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.662531

In an effort to further characterise the role of Stat3 in the self-renewal of ES cells, a screen to identify Stat3 molecules with altered activity was undertaken. This screen identified two Stat3 variants that were capable of maintaining ES cells in the absence of LIF. These molecules are Stat3β, a naturally occurring Stat3 isoform, and Stat3 Δ722, a C-terminal truncation of Stat3α. Both displayed indistinguishable effects on ES cell self-renewal, suggesting that increased Stat3β acts as a truncation of full-length Stat3α. Analysis of LIF-independent ES cell lines expressing increased Stat3β level confirmed the constitutive tyrosine phosphorylation and DNA binding activity of Stat3β. Cellular assays performed in the presence of a LIF receptor antagonist revealed that autocrine LIF signalling is not required for Stat3β-mediated ES cell self-renewal. Furthermore, biochemical analysis of Stat3β transfectants demonstrated that Stat3β acts to promote ES cell self-renewal without detectable Stat3α activity in the absence of LIF stimulation. These data indicate that Stat3β acts independently of Stat3α and is sufficient for ES cell maintenance. Further characterisation of Stat3β transfectants revealed additional effects. Differentiation of ES cells expressing increased Stat3β levels was suppressed <i>in vitro</i> and <i>in vivo</i>. Only when treated with potent pro-differentiation agents or when grafted into the kidney capsule of adult mice did Stat3β transfectants display any significant degree of differentiation. Increased Stat3β expression was also observed to correlate with a down-regulation of endogenous Stat3α expression. Quantitation of expression levels of both Stat3 isoforms in a range of cell lines revealed a consistent correlation, with increasing Stat3β levels associated with decreasing Stat3α levels. This suggests that Stat3β directly effects endogenous Stat3α expression.