C/EBP-β contains additional phosphorylation sites, C/EBP-βT188 and C/EBP-βS64 (Fig. 8B), which may be involved in modulating C/EBP-β-dependent SerpinB2 gene transcription. C/EBP-βT188 is implicated in regulating DAPK1, an IFNγ-inducible gene involved in the regulation of cell cycle and apoptosis [38], processes with which SerpinB2 has also been associated [17]. C/EBP-βS64 is important for LPS-induced transcription of the cytokines IL-6 and MCP-1 [64]. Similarly, SerpinB2 is induced by LPS and regulated in a manner similar to cytokines [29]. Given the similarities in the functional significance of these phospho-specific isoforms of C/EBP-β and SerpinB2, we investigated whether these phospho-acceptor sites may play a role in SerpinB2 gene expression. C/EBP-βT188A-transfected MEFs exhibited SerpinB2 promoter activity similar to that of wild-type C/EBP-β-transfected MEFs, whereas the expression of C/EBP-βS64A potentiated SerpinB2 promoter activity in response to LPS (Fig. 8C, right). These data suggest that phosphorylation of C/EBP-β at S64 acts to negatively regulate SerpinB2 proximal promoter activity.