Interestingly, microarray analysis revealed that genes such as SMAD3 and SMAD4, which are the principal intracellular effectors of the TGFB family, GADD45A and GADD45B, which are implicated as stress sensors and activated by TGFB in a SMAD dependent manner, DUSP1, DUSP5, DUSP6 and DUSP13, which are stress inducible MAP kinase phos phatases, MAP kinase kinase kinase Inhibitors,Modulators,Libraries 8, JUN, which is the effector transcription factor of the JNK pathway, and IL6, IL8 and FAS, which are in flammatory cytokines, were all upregulated by Tax. These genes, expressed in response to Tax, are media tors of JNK and p38 activity. In addition, we found that the kinetics of altered expression of several genes related to pathways involving stress responsive MAPKs were closely correlated with the kinetics of the spatial and temporal patterns of cell cycle dynamics analyzed in time lapse imaging.
At 24 h post transfection with Tax expression vectors, the genes for IL8, SMAD3, CDKN1A, GADD45A, GADD45B and IL6 were sig nificantly upregulated and the number of Tax IRES CFP expressing cells were in G1 phase and underwent apoptosis started to increase at same timing. Thus, the present results suggest that Tax may induce apoptosis Inhibitors,Modulators,Libraries and cell cycle arrest by activating several genes related to stress response signaling pathways. This is supported by a recent publication Anacetrapib showing that Tax, along with the activation of a stress kinase, can induce cell death. Furthermore, the present findings consist with those observed by previous microarray analysis stud ies of HTLV 1 infected T cells, which demonstrated that HTLV 1 infection upregulated JNK activation kinase 1, GADD45 and the inflammatory cytokine, IL1B, which are involved in MAPK stress response pathways.
Re cently, HTLV 1 Tax appeared indirectly to connect to cell cycle proteins such as SMAD3, SMAD4, GADD45A and GADD45B. Our microarray Inhibitors,Modulators,Libraries analysis results identified one of the genes upregulated by Tax as CDKN1A, which codes p21CIP1 WAF1, known as Cdk inhibitor 1. Again, this is in agreement with results Inhibitors,Modulators,Libraries from other microarray analyses showing that HTLV 1 infection and Tax expression upregulated p21CIP1 WAF1 in HTLV 1 infected T cells and the human Jurkat T cell line JPX 9, which ex press Tax under the control of an inducible promoter. Likewise, Tax has previously been shown to dra matically upregulate p21CIP1 WAF1 mRNA transcription and stabilization of p21CIP1 WAF1 in HeLa cells.
Interestingly, only minimal p21 WAF1 promoter activity appears to be induced by Tax. It is also known that basal levels of p21CIP1 WAF1 are required to promote TGFB mediated cell cycle arrest, whereas a lack of p21CIP1 WAF1 allows the induction of cell proliferation in response to TGFB. Indeed, the loss of p21CIP1 WAF1 and p27KIP1 from HOS cells apparently allows HTLV 1 and Tax induced G1 arrest to be bypassed.