CCND1 and renal cell carcinoma: Moreover, highly malignant RCC cells can pass circ-PRKCI to less malignant RCC cells via sEVs, and transferred circ-PRKCI acts as a sponge for miR-545-3p, increasing the expression of Cyclin D1 (CCND1), a cell cycle regulator associated with cell proliferation in a variety of tumor cells, and overexpression of CCND1 ultimately increased proliferation, migration and invasion of RCC cells (44).