The evolution of the histone methyltransferase gene Su(var)3-9 in metazoans includes a fusion with and a re-fission from a functionally unrelated gene

BACKGROUND: In eukaryotes, histone H3 lysine 9 (H3K9) methylation is a common mechanism involved in gene silencing and the establishment of heterochromatin. The loci of the major heterochromatic H3K9 methyltransferase Su(var)3-9 and the functionally unrelated γ subunit of the translation initiation factor eIF2 are fused in Drosophila melanogaster. Here we examined the phylogenetic distribution of this unusual gene fusion and the molecular evolution of the H3K9 HMTase Su(var)3-9. RESULTS: We show that the gene fusion had taken place in the ancestral line of winged insects and silverfishs (Dicondylia) about 400 million years ago. We cloned Su(var)3-9 genes from a collembolan and a spider where both genes ancestrally exist as independent transcription units. In contrast, we found a Su(var)3-9-specific exon inside the conserved intron position 81-1 of the eIF2γ gene structure in species of eight different insect orders. Intriguinly, in the pea aphid Acyrthosiphon pisum, we detected only sequence remains of this Su(var)3-9 exon in the eIF2γ intron, along with an eIF2γ-independent Su(var)3-9 gene. This reveals an evolutionary re-fission of both genes in aphids. Su(var)3-9 chromo domains are similar to HP1 chromo domains, which points to a potential binding activity to methylated K9 of histone H3. SET domain comparisons suggest a weaker methyltransferase activity of Su(var)3-9 in comparison to other H3K9 HMTases. Astonishingly, 11 of 19 previously described, deleterious amino acid substitutions found in Drosophila Su(var)3-9 are seemingly compensable through accompanying substitutions during evolution. CONCLUSION: Examination of the Su(var)3-9 evolution revealed strong evidence for the establishment of the Su(var)3-9/eIF2γ gene fusion in an ancestor of dicondylic insects and a re-fission of this fusion during the evolution of aphids. Our comparison of 65 selected chromo domains and 93 selected SET domains from Su(var)3-9 and related proteins offers functional predictions concerning both domains in Su(var)3-9 proteins

MicroRNA-210 induces apoptosis in colorectal cancer via induction of reactive oxygen

Additional file 2: Figure S2. Representative flow cytometric histograms of CRC cell lines 72 h post transfection with pre-miR-210 and a control miRNA, respectively. Cells were stained with by PI staining and subjected to FACS analysis

Perturbed myoepithelial cell differentiation in BRCA mutation carriers and in ductal carcinoma in situ.

Myoepithelial cells play key roles in normal mammary gland development and in limiting pre-invasive to invasive breast tumor progression, yet their differentiation and perturbation in ductal carcinoma in situ (DCIS) are poorly understood. Here, we investigated myoepithelial cells in normal breast tissues of BRCA1 and BRCA2 germline mutation carriers and in non-carrier controls, and in sporadic DCIS. We found that in the normal breast of non-carriers, myoepithelial cells frequently co-express the p63 and TCF7 transcription factors and that p63 and TCF7 show overlapping chromatin peaks associated with differentiated myoepithelium-specific genes. In contrast, in normal breast tissues of BRCA1 mutation carriers the frequency of p63+TCF7+ myoepithelial cells is significantly decreased and p63 and TCF7 chromatin peaks do not overlap. These myoepithelial perturbations in normal breast tissues of BRCA1 germline mutation carriers may play a role in their higher risk of breast cancer. The fraction of p63+TCF7+ myoepithelial cells is also significantly decreased in DCIS, which may be associated with invasive progression

Targeting Aberrant FGFR Signaling to Overcome CDK4/6 Inhibitor Resistance in Breast Cancer

Breast cancer (BC) is the most common cause of cancer-related death in women worldwide. Therapies targeting molecular pathways altered in BC had significantly enhanced treatment options for BC over the last decades, which ultimately improved the lives of millions of women worldwide. Among various molecular pathways accruing substantial interest for the development of targeted therapies are cyclin-dependent kinases (CDKs)\u2014in particular, the two closely related members CDK4 and CDK6. CDK4/6 inhibitors indirectly trigger the dephosphorylation of retinoblastoma tumor suppressor protein by blocking CDK4/6, thereby blocking the cell cycle transition from the G1 to S phase. Although the CDK4/6 inhibitors abemaciclib, palbociclib, and ribociclib gained FDA approval for the treatment of hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)- negative BC as they significantly improved progression-free survival (PFS) in randomized clinical trials, regrettably, some patients showed resistance to these therapies. Though multiple molecular pathways could be mechanistically responsible for CDK4/6 inhibitor therapy resistance, one of the most predominant ones seems to be the fibroblast growth factor receptor (FGFR) pathway. FGFRs are involved in many aspects of cancer formation, such as cell proliferation, differentiation, and growth. Importantly, FGFRs are frequently mutated in BC, and their overexpression and/or hyperactivation correlates with CDK4/6 inhibitor resistance and shortened PFS in BC. Intriguingly, the inhibition of aberrant FGFR activity is capable of reversing the resistance to CDK4/6 inhibitors. This review summarizes the molecular background of FGFR signaling and discusses the role of aberrant FGFR signaling during cancer development in general and during the development of CDK4/6 inhibitor resistance in BC in particular, together with other possible mechanisms for resistance to CDK4/6 inhibitors. Subsequently, future directions on novel therapeutic strategies targeting FGFR signaling to overcome such resistance during BC treatment will be further debated

Increased lysosomal biomass is responsible for the resistance of triple-negative breast cancers to CDK4/6 inhibition

Breast cancer is the most common type of cancer in women and the second leading cause of cancer death among women. While significant progress has been made in the treatment of hormone receptor (HR) positive, HER2 negative and HER2-amplified breast cancer in the last decades, Triple negative breast cancer (TNBC) is lacking behind. Still today, chemotherapy is the only treatment option, but response rates are low and only a small fraction of patients can successfully be treated. Here we show, that CDK4/6 inhibitors which are FDA-approved for the treatment of HR+/HER2negative breast cancer and significantly improved treatment outcome in this type of breast cancer, also represent a promising therapy option for TNBC in contrast to the current view. We show, that a subset of TNBCs despite being resistant to chemical inhibition of CDK4/6 strictly depend on CDK4/6 kinases for proliferation. We identified lysosomal sequestration of the drug and therefore limited bioavailability at its target site responsible for the discrepancy. We show that increased number of lysosomes correlates with resistance and inhibition of the lysosome renders these cells fully sensitive to CDK4/6 inhibitors. We provide strategies how to overcome resistance by means of FDA-approved lysosomotropic agents that raise lysosomal pH, co-inhibition of CDK2 or the use of structurally altered CDK4/6 inhibitors with decreased basic characteristics. We also provide a biomarker to stratify patients for successful CDK4/6 inhibitor therapy. Moreover, we show that this mechanism of resistance also underlies cases of acquired resistance in HR+/HER2negative breast cancer and importantly we provide evidence that increased lysosomal sequestration operates in patients presenting resistant to treatment with the CDK4/6 inhibitor palbociclib. Our study therefore suggests that CDK4/6 inhibitor therapy could be a treatment option for a subset of TNBCs where new targeted therapeutic intervention is so urgently needed and furthermore, offers strategies how to overcome resistance in HR+/HER2-negative breast cancer where CDK4/6 inhibition is already successfully applied. In summary, our study provides ways on how to improve therapeutic use of this promising new class of anti-cancer agents

Targeting the cyclin-dependent kinase 5 in metastatic melanoma

© 2020 National Academy of Sciences. All rights reserved. The cyclin-dependent kinase 5 (CDK5), originally described as a neuronal-specific kinase, is also frequently activated in human cancers. Using conditional CDK5 knockout mice and a mouse model of highly metastatic melanoma, we found that CDK5 is dispensable for the growth of primary tumors. However, we observed that ablation of CDK5 completely abrogated the metastasis, revealing that CDK5 is essential for the metastatic spread. In mouse and human melanoma cells CDK5 promotes cell invasiveness by directly phosphorylating an intermediate filament protein, vimentin, thereby inhibiting assembly of vimentin filaments. Chemical inhibition of CDK5 blocks the metastatic spread of patient-derived melanomas in patient-derived xenograft (PDX) mouse models. Hence, inhibition of CDK5 might represent a very potent therapeutic strategy to impede the metastatic dissemination of malignant cells

Cell-Cycle-Targeting MicroRNAs as Therapeutic Tools against Refractory Cancers

Cyclins and cyclin-dependent kinases (CDKs) are hyperactivated in numerous human tumors. To identify means of interfering with cyclins/CDKs, we performed nine genome-wide screens for human microRNAs (miRNAs) directly regulating cell-cycle proteins. We uncovered a distinct class of miRNAs that target nearly all cyclins/CDKs, which are very effective in inhibiting cancer cell proliferation. By profiling the response of over 120 human cancer cell lines, we derived an expression-based algorithm that can predict the response of tumors to cell-cycle-targeting miRNAs. Using systemic administration of nanoparticle-formulated miRNAs, we inhibited tumor progression in seven mouse xenograft models, including three treatment-refractory patient-derived tumors, without affecting normal tissues. Our results highlight the utility of using cell-cycle-targeting miRNAs for treatment of refractory cancer types. Keywords: cell cycle; cyclins; cyclin-dependent kinases; microRNAs; cancer