Identifikation von miRNAs und ihrer Zielmoleküle mit Bedeutung für die chronische lymphatische Leukämie
Final Report Abstract
Malignant melanoma is the most dangerous form of skin cancer. Once it metastasizes it becomes a highly lethal and frequently drug refractory cancer. Even though much is known about oncogenic pathways in melanoma and even though drugs exist that target some of the key players in these pathways, it has not yet been possible to significantly increase the survival rate of patients with metastatic melanoma. New diagnostic and therapeutic options are urgently needed. MicroRNAs are a class of endogenous, small, non-coding RNAs that naturally regulate a variety of biological phenomena. One of these miRN/Vs, miR-211, is found only in melanocytes. It is expressed from an intron of the putative melanocytespecific tumor suppressor gene, melastatin, also known as TRPM1. Interestingly, reduced expression of melastatin predicts increased metastatic potential and aggressiveness of malignant melanoma. Surprisingly, it was found in this research project that manipulation of the levels of miR-211 is sufficient to change the invasive potential - a prerequisite for metastasis - of melanoma samples in vitro. This effect of the miRNA is independent of its host gene TRPM1. We report that melanomas with very low expression of miR- 21 1 display increased invasive activity. Importantly, artificial expression of miR-211 in these melanomas reduces their invasive activity in vitro. Conversely, in melanomas with higher levels of miR-211, inhibition of miR-211 increases invasive activity. Knockdown of melastatin, however, does not affect invasive activity. Therefore, the data raise the possibility that earlier observations relating TRPM1 expression to the aggressiveness of melanoma may have in fact been due to expression of miR-211. In addition, evidence was obtained that this effect of miR-211 is at least partially mediated through regulation of the protein kinase ARK5. It was found that miR-211 targets ARK5 and that knockdown of ARK5 phenocopies ectopic expression of miR-211. These data indicate that reduced expression of miR-211, and not melastatin, affects early events during melanoma metastasis. Our data suggest that miR-211 may be useful for differential diagnosis and detection of particular melanoma variants with metastatic potential. Moreover, targeting miR-211 directly may pave the way towards new therapies of metastatic melanoma.
