The E2F1-HOXB9/PBX2-CDK6 axis drives gastric tumorigenesis and serves as a therapeutic target in gastric cancer.

Homeobox genes include HOX and non-HOX genes. HOX proteins play fundamental roles during ontogenesis by interacting with other non-HOX gene-encoded partners and performing transcriptional functions, whereas aberrant activation of HOX family members drives tumorigenesis. In this study, gastric cancer (GC) expression microarray data indicated that HOXB9 is a prominent upregulated HOX member in GC samples significantly associated with clinical outcomes and advanced TNM stages. However, the functional role of HOXB9 in GC remains contradictory in previous reports, and the regulatory mechanisms are elusive. By in silico and experimental analyses, we found that HOXB9 was upregulated by a vital cell cycle-related transcription factor, E2F1. Depleting HOXB9 causes G1-phase cell cycle arrest by downregulating CDK6 and a subset of cell cycle-related genes. Meanwhile, HOXB9 contributes to cell division and maintains the cytoskeleton in GC cells. We verified that HOXB9 interacts with PBX2 to form a heterodimer, which transcriptionally upregulates CDK6. Knocking down CDK6 can phenocopy the tumor-suppressive effects caused by HOXB9 depletion. Blocking HOXB9 can enhance the anti-tumor effect of CDK6 inhibitors. In conclusion, we elucidate the oncogenic role of HOXB9 in GC and reveal CDK6 as its potent downstream effector. The E2F1-HOXB9/PBX2-CDK6 axis represents a novel mechanism driving gastric carcinogenesis and conveys prognostic and therapeutic implications. © 2023 The Pathological Society of Great Britain and Ireland.

Cancer-associated fibroblasts potentiate colorectal cancer progression by crosstalk of the IGF2-IGF1R and Hippo-YAP1 signaling pathways.

Colorectal cancer (CRC) is one of the most common cancers worldwide. The tumor microenvironment exerts crucial effects in driving CRC progression. Cancer-associated fibroblasts (CAFs) serve as one of the most important tumor microenvironment components promoting CRC progression. This study aimed to elucidate the novel molecular mechanisms of CAF-secreted insulin-like growth factor (IGF) 2 in colorectal carcinogenesis. Our results indicated that IGF2 was a prominent factor upregulated in CAFs compared with normal fibroblasts. CAF-derived conditioned media (CM) promoted tumor growth, migration, and invasion of HCT 116 and DLD-1 cells. IGF1R expression is significantly increased in CRC, serving as a potent receptor in response to IGF2 stimulation and predicting unfavorable outcomes for CRC patients. Apart from the PI3K-AKT pathway, RNA-seq analysis revealed that the YAP1-target signature serves as a prominent downstream effector to mediate the oncogenic signaling of IGF2-IGF1R. By single-cell RNA sequencing (scRNA-seq) and immunohistochemical validation, IGF2 was found to be predominantly secreted by CAFs, whereas IGF1R was expressed mainly by cancer cells. IGF2 triggers the nuclear accumulation of YAP1 and upregulates YAP1 target signatures; however, these effects were abolished by either IGF1R knockdown or inhibition with picropodophyllin (PPP), an IGF1R inhibitor. Using CRC organoid and in vivo studies, we found that cotargeting IGF1R and YAP1 with PPP and verteporfin (VP), a YAP1 inhibitor, enhanced antitumor effects compared with PPP treatment alone. In conclusion, this study revealed a novel molecular mechanism by which CAFs promote CRC progression. The findings highlight the translational potential of the IGF2-IGF1R-YAP1 axis as a prognostic biomarker and therapeutic target for CRC. © 2022 The Pathological Society of Great Britain and Ireland.