The development of resistance and the activation of bypass pathway signalling represents a major problem for the clinical application of protein kinase inhibitors. While investigating the effect of either a c-Rel deletion or RelAT505A phosphosite knockin on the Eµ-Myc mouse model of B-cell lymphoma, we discovered that both NF-κB subunit mutations resulted in CHK1 inhibitor resistance, arising from either loss or alteration of CHK1 activity, respectively. However, since Eµ-Myc lymphomas depend on CHK1 activity to cope with high levels of DNA replication stress and consequent genomic instability, it was not clear how these mutant NF-κB subunit lymphomas were able to survive. To understand these survival mechanisms and to identify potential compensatory bypass signalling pathways in these lymphomas, we applied a multi-omics strategy. With c-Rel−/− Eµ-Myc lymphomas we observed high levels of Phosphatidyl-inositol 3-kinase (PI3K) and AKT pathway activation. Moreover, treatment with the PI3K inhibitor Pictilisib (GDC-0941) selectively inhibited the growth of reimplanted c-Rel−/− and RelAT505A, but not wild type (WT) Eµ-Myc lymphomas. We also observed up-regulation of a RHO/RAC pathway gene expression signature in both Eµ-Myc NF-κB subunit mutation models. Further investigation demonstrated activation of the RHO/RAC effector p21-activated kinase (PAK) 2. Here, the PAK inhibitor, PF-3758309 successfully overcame resistance of RelAT505A but not WT lymphomas. These findings demonstrate that up-regulation of multiple bypass pathways occurs in CHK1 inhibitor resistant Eµ-Myc lymphomas. Consequently, drugs targeting these pathways could potentially be used as either second line or combinatorial therapies to aid the successful clinical application of CHK1 inhibitors.

Plasma alpha-melanocyte stimulating hormone (alpha-MSH) concentrations were measured in patients receiving PUVA therapy as treatment for mycosis fungoides, and PUVA or UVB as treatment for psoriasis. Skin immunoreactive alpha-MSH was also measured in those patients who received PUVA. The mean plasma and skin alpha-MSH concentrations after 2-3 weeks of PUVA were not significantly different from pre-treatment values and showed no relationship either to skin type or to the degree of tanning that occurred in response to PUVA. Plasma alpha-MSH concentrations were also unchanged after UVB. There was also no short term change in plasma alpha-MSH concentrations in patients after receiving their first treatment with PUVA. It would appear that circulating and skin alpha-MSH levels are unaffected by UV and show no causal relationship to PUVA induced pigmentation.

Heterochromatin is characterized by specific histone post-translational modifications such as the di- and tri-methylation of histone H3 on lysine 9 (H3K9me2/3), which direct the recruitment of reader proteins to chromatin. In the fungal phytopathogen, Zymoseptoria tritici, deletion of the H3K9 methyltransferase gene kmt1, results in a global increase in the expression of transposable elements (TEs), genome instability and loss of virulence. Here we have identified two Z. tritici chromodomain proteins, Cbx1 and Cbx2, that recognise H3K9me modifications. Cbx1 is a Heterochromatin Protein 1 homolog that binds H3K9me2/3 in vitro and associates with heterochromatic loci in vivo. Transcriptomic analysis also indicates that Cbx1 and Kmt1 regulate overlapping sets of protein-encoding genes. However, unlike Δkmt1 mutants, Δcbx1 strains do not exhibit a global increase in TE expression and have only a partial reduction in virulence, suggesting the existence of additional H3K9me reader proteins. Accordingly, we have identified a fungal-specific chromodomain protein, Cbx2, that binds H3K9me3 in vitro. Strikingly, the growth defects of Δcbx1 Δcbx2 double mutants closely resemble those of Δkmt1 consistent with Cbx1 and Cbx2 playing redundant roles in gene silencing. Overall, the data suggest that key functions of H3K9me modifications are mediated by a combination of Cbx1 and Cbx2

Heterochromatin is a repressive chromatin state that plays key roles in the functional organisation of eukaryotic genomes. In fungal plant pathogens, effector genes that are required for host colonization tend to be associated with heterochromatic regions of the genome that are enriched with transposable elements. It has been proposed that the heterochromatin environment silences effector genes in the absence of host and dynamic chromatin remodelling facilitates their expression during infection. Here we discuss this model in the context of the key wheat pathogen, Zymoseptoria tritici. We cover progress in understanding the deposition and recognition of heterochromatic histone post translational modifications in Z. tritici and the role that heterochromatin plays in control of genome plasticity and virulence.