Our laboratory performs research on (1) the transcriptional regulation of primary response genes (eg.junB) by IL-6 and other mediators (eg. cytokines, LPS), and (2) the molecular pathways involved in IL-6 signalling and plasmacytoma growth, including the identification of alterations that lead to cytokine-independent tumor growth. We have established an extensive and unique library of luciferase reporter constructs containing elements from both the 5' and 3' regulatory regions surrounding the primary response gene junB. We have previously documented a novel 222 base pair multi-site enhancer region downstream of the junB coding region that both upregulates the junB promotor (75-fold) and confers inducibility by IL-6 in plasmacytomas. Extensive mutational and DNA-binding analyses reveal a key role for a novel STAT3 site. We have recently determined this site alone is insufficient to drive IL-6-inducible transcription We are currently characterizing the contribution and interaction of adjacent elements within this novel enhancer region that cooperate with STAT3. In a related study, we have also initiated studies to define the transcription factors responsible for the activation of junB in macrophages by LPS. Our plasmacytoma studies indicate that the transition to IL-6-independence (a key step in the malignant progression of these tumors) is not an autocrine mechanism. junB transcription is constitutively active in independent cells, and DNA-binding and transient expression studies indicate that the loss of growth factor dependence is associated with constitutive activation of STAT3. Thus, the alterations leading to independent growth appear to be """"""""upstream"""""""" of the activation of the STAT3 transcription factor and the transcriptional activation of junB, but do not involve signalling through the IL-6 receptor complex. The ability to restore IL-6-dependence to IL-6-independent plasmacytomas by the introduction of normal DNA with normal lymphocytes (eg. classic B-cell hybridomas) suggests that the transition to growth fctor independence may involve the inactivation or functional loss of a negative growth regulatory/tumor suppressor gene. Identification of the alterations responsible for the IL-6-independence mechanism is underway.
