Endogenous myoglobin in breast cancer is hypoxia-inducible by alternative transcription and functions to impair mitochondrial activity: a role in tumor suppression?

Recently, immunohistochemical analysis of myoglobin (MB) in human breast cancer specimens has revealed a surprisingly widespread expression of MB in this nonmuscle context. The positive correlation with hypoxia-inducible factor 2α (HIF-2α) and carbonic anhydrase IX suggested that oxygen regulates myoglobin expression in breast carcinomas. Here, we report that MB mRNA and protein levels are robustly induced by prolonged hypoxia in breast cancer cell lines, in part via HIF-1/2-dependent transactivation. The hypoxia-induced MB mRNA originated from a novel alternative transcription start site 6 kb upstream of the ATG codon. MB regulation in normal and tumor tissue may thus be fundamentally different. Functionally, the knockdown of MB in MDA-MB468 breast cancer cells resulted in an unexpected increase of O(2) uptake and elevated activities of mitochondrial enzymes during hypoxia. Silencing of MB transcription attenuated proliferation rates and motility capacities of hypoxic cancer cells and, surprisingly, also fully oxygenated breast cancer cells. Endogenous MB in cancer cells is apparently involved in controlling oxidative cell energy metabolism, contrary to earlier findings on mouse heart, where the targeted disruption of the Mb gene did not effect myocardial energetics and O(2) consumption. This control function of MB seemingly impacts mitochondria and influences cell proliferation and motility, but it does so in ways not directly related to the facilitated diffusion or storage of O(2). Hypothetically, the mitochondrion-impairing role of MB in hypoxic cancer cells is part of a novel tumor-suppressive function.

The androgen-regulated Calcium-Activated Nucleotidase 1 (CANT1) is commonly overexpressed in prostate cancer and is tumor-biologically relevant in vitro.

Previously, we identified the calcium-activated nucleotidase 1 (CANT1) transcript as up-regulated in prostate cancer. Now, we studied CANT1 protein expression in a large cohort of nearly 1000 prostatic tissue samples including normal tissue, prostatic intraepithelial neoplasia (PIN), primary carcinomas, metastases, and castrate-resistant carcinomas, and further investigated its functional relevance. CANT1 displayed predominantly a Golgi-type immunoreactivity with additional and variable cytoplasmic staining. In comparison to normal tissues, the staining intensity was significantly increased in PIN lesions and cancer. In cancer, high CANT1 levels were associated with a better prognosis, and castrate-resistant carcinomas commonly showed lower CANT1 levels than primary carcinomas. The functional role of CANT1 was investigated using RNA interference in two prostate cancer cell lines with abundant endogenous CANT1 protein. On CANT1 knockdown, a significantly diminished cell number and DNA synthesis rate, a cell cycle arrest in G(1) phase, and a strong decrease of cell transmigration rate and wound healing capacity of CANT1 knockdown cells was found. However, on forced CANT1 overexpression, cell proliferation and migration remained unchanged. In summary, CANT1 is commonly overexpressed in the vast majority of primary prostate carcinomas and in the precursor lesion PIN and may represent a novel prognostic biomarker. Moreover, this is the first study to demonstrate a functional involvement of CANT1 in tumor biology.

Modelling of a genetically diverse evolution of Systemic Mastocytosis with Chronic Myelomonocytic Leukemia (SM-CMML) by Next Generation Sequencing.

BACKGROUND: Systemic mastocytosis (SM) is a heterogenous, clonal mast cell (MC) proliferation, rarely associated with clonal hematologic non-mast cell lineage disease (SM-AHNMD). KIT (D816V) is regarded as driver-mutation in SM-AHNMD. METHODS: DNA isolated from peripheral blood (PB) of an SM-CMML patient was investigated with targeted next generation sequencing. Variants were verified by Sanger sequencing and further characterized in the SM part of the bone marrow trephine (BMT), normal tissue, and FACS sorted PB cell subpopulations. FINDINGS: Low coverage deep-sequencing (mean 10x) on a GS 454 Junior revealed two as yet unreported SNVs (CBFA2T3 and CLTCL1), both germ-line mutations. High coverage (mean 1674x) targeted re-sequencing on an Ion Proton revealed 177 variants in coding regions. Excluding SNPs, the final list comprised 11 variants. Among these, TET2 (p.Thr1027fs, p.Cys1263Ser) and RUNX1 (p.Asn109Ser) were identified in in the peripheral blood and the SM part of BMT, but not in normal tissue. Furthermore, Sanger sequencing of PB cells revealed similar signal intensities for both TET2 mutations in FACS sorted CD34+ precursor cells and CD16+ granulocytes comparable to signals in the SM part of BMT. In contrast, RUNX1 exhibited a double intensity in CD34+ cells compared to the SM part of BMT and a homozygous variant signal in granulocytes. Both TET2 and RUNX1 mutations were not detectable in B- and T-cells. CONCLUSION: We present a heterozygous triple-mutation pattern (KIT, TET2, RUNX1) in mast cells (SM disease part) with additional LOH of RUNX1 in granulocytes (CMML disease part). These identified mutations allow a more detailed insight into a multistep pathogenesis which suggests a common tumor progenitor in SM-CMML.