No abstract

PNC-2 and PNC-7 peptides induce phenotypic reversion of ras-induced pancreatic cancer cells and have no effect on normal pancreatic cell growth. Since the plasmid encoding PNC-2 without penetratin also had the same effect on the TUC-3 cell line, we conclude that the penetratin sequence has no effect on the activity of this peptide. Since X13 attached to penetratin had no effect on TUC-3 cells, the effect is specific for PNC-2 and PNC-7 and further confirms that the effect is not caused by the penetratin sequence. PNC-2- and PNC-7-penetratin may therefore be useful in the treatment of ras-induced pancreatic carcinomas.

BSAP (Pax5) is a transcription factor expressed exclusively in the developing midbrain, testes, pro-B cells, pre-B cells, and mature B cells (1). When the Pax5 gene was inactivated in mice by targeted homologous recombination, defects in the midbrain and in B cell lymphopoiesis were observed, including complete abrogation of fetal B lymphopoiesis and incomplete VH gene construction in adult bone marrow (2). Recent studies have reported that preBI cells from BSAP -/-mice can differentiate in culture or in some cases, in vivo, to a variety of non-B cell types, including macrophages, granulocytes, osteoclasts, T cells, and natural killer cells (3). This suggests a role for BSAP not only in promoting B cell development but also in eliminating other developmental possibilities.Some target genes for BSAP have been identified (reviewed in Ref. 4), including CD19, LEF, N-myc, mb-1, and PD1, although these are unlikely to be critical for B cell development (5). BSAP is active later in B cell development, potentially through binding sites in murine heavy (6) and light chain 3Ј enhancers (7), J chain, (8), blk (9), CD72 (10), and RAG-2 promoter (11). A number of observations suggest that BSAP function can be modulated by its interaction with other proteins. For example, it has been shown that BSAP down-regulates the murine 3Ј IgH enhancer hs1,2 in B cell lines in concert with other transcription factors that also bind to this enhancer (12). These factors include octamer-binding proteins, B-binding proteins, and a G-rich DNA-binding protein. Using a GST 1 pulldown assay, we detected interaction of BSAP with the POU domains of Oct-1 and Oct-2 (12). Other investigators have shown that the DNA-binding domain of BSAP interacts with and recruits Ets family proteins to ternary complexes with the mb-1 promoter in pre-B cells (13). BSAP has also been shown to interact with the acute myeloid leukemia protein, AML, in the regulation of the blk promoter (9) and with PU.1 (14). We have therefore proposed to identify proteins that interact with BSAP using a yeast two-hybrid assay.BSAP is a member of the highly conserved Using the central domain of BSAP as a bait in the two-hybrid assay system, we report here a strong interaction with Rch1

We conclude that there is a strong reciprocal interaction between the SAP pathway involving JNK and the raf-MEK-MAP kinase pathway and that oncogenic ras-p21 can be preferentially inhibited by MEK inhibitors. The results imply that blockade of both MEK and JNK-oncogenic ras-p21 interactions may constitute selective synergistic combination chemotherapy against oncogenic ras-induced tumors.

We conclude that the PNC2 plasmid selectively inhibits oncogenic ras-p21 and may therefore be highly effective in blocking proliferation of ras-induced cancer cells. Also, from the patterns of inhibition, by PNC2 and other ras- and raf-related peptides, of raf- and constitutively activated MEK-induced maturation, we conclude that PNC2 peptide inhibits oncogenic ras p21 downstream of raf.