Tumour-Associated MUC1 Exerts Multiple Effects on Cholesterol and Lipid Metabolism—A Potential Pathogenic Effector of Atherosclerosis in Cancer

(1) Cancer has been shown to contribute to the progression of atherosclerosis, while inflammatory aspects of atherosclerosis can exert profound effects on cancer development and outcomes. TA-MUC1 (Tumour-associated Mucin 1) is a transmembrane glycoprotein that is overexpressed in many human epithelial cancers lining the intestine. Interestingly, the lack of intestinal MUC1 has been shown to impair cholesterol uptake in MUC1^-/- mice. (2) To investigate whether TA-MUC1 could have specific effects on cholesterol metabolism and, thereby, have the potential of impacting the pathogenesis of atherosclerosis in cancer patients. (3) The effect of TA-MUC1 on cholesterol and lipid metabolism was assayed using MUC1 gene knock down breast cancer cells. An in vitro coculturing model similar to in vivo biological conditions was used to determine that TA-MUC1 could also modulate the cholesterol metabolism of other cells. (4) Reduction or inhibition of TA-MUC1 activity resulted in a significant alteration in a number of the signalling pathways and proteins that are relevant to abnormal cholesterol metabolism (<i>p</i> < 0.0001). Coculturing of TA-MUC1 cancer cells with THP-1 cells also notably effectively induced monocytic THP-1 cell differentiation towards foam cells-foam cells being a characteristic feature of atherosclerotic blood vessels. (5) Previously, we found TA-MUC1 downregulation led to a reduction in procoagulant and prothrombotic properties of the cancer cells as well as modulation of the aberrant calcium signalling pathways of cancer cells. Taken together with these current results, this suggests that TA-MUC1 in cancer cells has multiple effects on cholesterol and lipid metabolism, which also impacts other cells in the cellular bioenvironment. TA-MUC1 could thereby act as an important pathogenic effector of atherosclerosis in cancer. These results can also be considered in respect of the therapeutic anti-MUC1 antibody, which was able to reduce the effect of TA-MUC1 on cholesterol metabolism. Modulation of cholesterol metabolism via targeting TA-MUC1 could, therefore, be of great benefit to cancer patients with atherosclerosis.