PIWIL1 is recruited to Centrosomes during Mitosis in Colorectal Cancer Cells and is linked to cell cycle progression

PIWI proteins, traditionally associated with germline development, have recently gained attention for their expression in various cancers, including colorectal cancer (CRC). However, the molecular mechanisms underlying their reactivation and impact on cancer initiation and progression remain elusive. Here, we found that PIWIL1 is expressed at relatively high levels in CRC-derived samples and cell lines, where it undergoes a dynamic re-localization to the centrosome during mitosis. Knockdown of PIWIL1 induces G2/M arrest associated to disruption of mitotic spindle and aberrant metaphase events, highlighting its role in cell cycle progression. We have also found that expression of PIWIL1 is lost during differentiation of Caco-2 cells into enterocytes and that PIWIL1 is expressed in cells at the base of intestinal crypts in normal human colon tissue, where intestinal stem cells are known to reside. Thus, it is possible that the presence of PIWIL1 in cancer cells reflects a physiological role of this protein in stem cell maintenance, what would argue in favor of the proposed stem cell origin of CRC. Supporting this view, dedifferentiation of human fibroblasts into induced pluripotent stem cells (iPSc) implies reactivation of PIWIL2 expression, another member of the PIWI protein family. Overall, our findings suggest a role of PIWIL1 in mediating cell cycle dynamics, both in colorectal cancer cells and possibly also in intestinal stem cells. In a broader aspect, we provide support for an involvement of PIWI proteins in somatic stem cell maintenance, expanding nongonadal functions for this protein family.