Rates of colon cancer are much higher in African Americans (65:100,000) than in rural South Africans (<5:100,000). The higher rates are associated with higher animal protein and fat and lower fiber consumption, higher colonic secondary bile acids, lower colonic short chain fatty acid quantities and higher mucosal proliferative biomarkers of cancer risk in otherwise healthy middle aged volunteers. Here we investigate further the role of fat and fiber in this association. We performed two-week food exchanges in subjects from the same populations, where African Americans were fed a high-fiber, lowfat African-style diet, and rural Africans a high-fat low-fiber western-style diet under close supervision. In comparison to their usual diets, the food changes resulted in remarkable reciprocal changes in mucosal biomarkers of cancer risk and in aspects of the microbiota and metabolome known to affect cancer risk, best illustrated by increased saccharolytic fermentation and butyrogenesis and suppressed secondary bile acid synthesis in the African Americans.

Antigen recognition by the T-cell receptor (TCR) initiates events including lymphokine gene transcription, particularly interleukin-2, that lead to T-cell activation. The immunosuppressive drugs, cyclosporin A (CsA) and FK-506, prevent T-cell proliferation by inhibiting a Ca(2+)-dependent event required for induction of interleukin-2 transcription. Complexes of FK-506 or CsA and their respective intracellular binding proteins inhibit the calmodulin-dependent protein phosphatase, calcineurin, in vitro. The pharmacological relevance of this observation to immunosuppression or drug toxicity is undetermined. Calcineurin, although present in lymphocytes, has not been implicated in TCR-mediated activation of lymphokine genes or in transcriptional regulation in general. Here we report that transfection of a calcineurin catalytic subunit increases the 50% inhibitory concentration (IC50) of the immunosuppressants FK-506 and CsA, and that a mutant subunit acts in synergy with phorbol ester alone to activate the interleukin-2 promoter in a drug-sensitive manner. These results implicate calcineurin as a component of the TCR signal transduction pathway by demonstrating its role in the drug-sensitive activation of the interleukin-2 promoter.

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The quinazolinone and pyridol-pyrimidine classes of p38 MAP kinase inhibitors have a previously unseen degree of specificity for p38 over other MAP kinases. Comparison of the crystal structures of p38 bound to four different compounds shows that binding of the more specific molecules is characterized by a peptide flip between Met109 and Gly110. Gly110 is a residue specific to the alpha, beta and gamma isoforms of p38. The delta isoform and the other MAP kinases have bulkier residues in this position. These residues would likely make the peptide flip energetically unfavorable, thus explaining the selectivity of binding. To test this hypothesis, we constructed G110A and G110D mutants of p38 and measured the potency of several compounds against them. The results confirm that the selectivity of quinazolinones and pyridol-pyrimidines results from the presence of a glycine in position 110. This unique mode of binding may be exploited in the design of new p38 inhibitors.

The interleukin-2 (IL-2) promoter consists of several independent T cell receptor (TcR) responsive elements. The induction of promoters dependent on these elements is inhibitable by the immunosuppressants cyclosporin A (CsA) and tacrolimus . Calcineurin, a Ca2+/calmodulin-dependent protein phosphatase, is the FK-506-and CsA-sensitive enzyme required for TcR mediated activation of the LL-2 promoter. We report that a constitutively active form of calcineurin partially substitutes for the Ca2+ co-stimulus required to activate the IL-2 promoter elements IL-2A (which binds the factors OAP and Oct-i) and LL-2E (which binds NF-AT), and completely substitutes for the Ca2+ co-stimulus required to stimulate an NF-xB-dependent element. Calcineurin stimulates the NF-xB element by enhancing inactivation of IxB/MAD3, an inhibitor of NF-xB, thereby increasing the amount of nuclear NF-xB DNA binding activity. These data provide the first demonstration in vivo that activation of a protein phosphatase can inactivate IxB, and suggest one possible explanation for mechanism-based toxicities associated with FK-506 and CsA by demonstrating that these drugs can inhibit the calcineurin-dependent activation of a virtually ubiquitous transcription factor.