Regulation of cellular growth and identification of stromal gene signatures in breast cancer

Sammanfattning: Normal tissue is tightly controlled to keep a balance between reproduction and elimination of cells. In cancer, these regulated processes are disrupted, resulting in uncontrolled cell growth. Regulation of RNA stability and turnover is important to maintain cellular homeostasis and can be controlled by various mechanisms. During stress, the cell can form cytoplasmic complexes of proteins and RNAs, called stress granules, to inhibit translation of proteins unnecessary for the cell during harmful conditions and focus translation on stress-related proteins. In neuroblastoma and breast cancer cell lines, we have found that the protein kinase C? (PKC?) isoform can influence stress granule formation in a stress inducer-specific way. Depletion of PKC? led to a delayed stress response along with an initial loss of eIF2? phosphorylation in heat shock, but not arsenite, treated cells. G3BP proteins are well-known stress inducers and we identified a direct interaction between PKC? and the G3BP2 isoform. G3BP2 belongs to a family of three homologous proteins with RNA-regulating capacities. With the aim to identify specific RNA targets, we performed a gene expression analysis and detected a negative regulation of the peripheral myelin protein (PMP22) by the G3BP1 isoform. The previously reported growth suppressing effects by PMP22 was here verified in breast cancer cells and we could show that G3BP1 influences growth regulation by reducing PMP22 expression, although not through mRNA destabilizing mechanisms. Another RNA regulating mechanism that can promote or prevent tumor progression are mRNA silencing through miRNA. We analyzed miR-34c and its function in breast cancer and identified impaired cell growth, induced apoptosis and cell cycle G2/M arrest, which might be due to regulation of the anaphase-promoting complex protein Cdc23. The tumor is not a homogenous compartment, but consists of various different cell types, both among the cancer cells as well as in the surrounding stroma. We have developed a methodological procedure for isolation and characterization of cancer- and stroma-specific genes using laser capture microdissection on FFPE triple negative breast cancers. Gene expression microarrays of these samples revealed compartment specific gene expression and enabled identification of stromal-specific gene signatures with tumor-predictive capacity.