Cytoplasmic p27 localization linked to WT KRAS expression in colorectal cancer progression

Colorectal cancer (CRC) remains a significant global health challenge, with diverse molecular subtypes influencing prognosis and treatment. The cyclin-dependent kinase inhibitor p27 (CDKN1B) is a well-known tumor suppressor that typically functions in the nucleus to regulate cell cycle progression. However, p27 can acquire oncogenic properties when mislocalized to the cytoplasm, often driven by post-translational modifications like phosphorylation. While KRAS mutations are known to induce p27 phosphorylation and cytoplasmic retention, the regulatory mechanisms and clinical significance of p27 expression and localization in wild-type (WT) KRAS CRC — which constitutes a substantial portion of cases — have remained largely unexplored, representing a critical knowledge gap in understanding CRC pathogenesis.

This study investigated p27 expression and localization in wild-type (WT) KRAS colorectal cancer (CRC). Researchers performed immunohistochemical analysis on 50 WT KRAS CRC tumor samples and their adjacent normal tissues. The primary objective was to assess the subcellular distribution of p27 and its correlation with WT KRAS status. Additionally, the study explored potential regulatory factors, including miR-221/222 expression levels and the presence of the CDKN1B V109G polymorphism, to determine their association with p27 levels and overall CRC susceptibility. Tissue sections were stained and analyzed to quantify p27-positive cells and their localization within different tissue compartments.

p27 expression patterns varied significantly across tissue types. The highest percentage of p27-positive cells was observed in the superficial layer of normal mucosa, while significantly fewer p27-positive cells were detected in the tumor center of WT KRAS CRCs. Crucially, WT KRAS tumors that also exhibited KRAS expression showed an increase in overall p27 expression.

Furthermore, these WT KRAS tumors displayed a predominant cytoplasmic localization of p27 specifically at the invasive front, suggesting a shift from its nuclear tumor-suppressive role. The study found no discernible correlation between miR-221/222 expression levels and p27 levels, indicating these microRNAs may not be primary regulators of p27 in this context. Similarly, the CDKN1B V109G polymorphism was not found to be associated with an increased risk of colorectal cancer. These findings highlight a novel mechanism of p27 dysregulation in WT KRAS CRC.