Tumor-associated macrophages (TAMs) play a pivotal role in shaping the tumor microenvironment. Lactic acid (LA) has been identified as an influential factor in promoting immune escape and tumor progression. However, the mechanisms through which LA modulates TAMs in colorectal cancer (CRC) remain poorly understood. We used qRT-PCR to quantify the expression of LA-related genes (LDHA and LAMP2) in CRC tumor tissues and adjacent nontumor tissues (n = 64). The biological effects and mechanisms of LA on macrophages and tumors were evaluated via qRT-PCR, Western blot, RNA-seq, wound healing assay, colony formation assay in vitro, and allograft mouse tumor models in vivo. We found the expression of LDHA and LAMP2 was highly elevated in the tumor regions and positively associated with a poor clinical stage of CRC. A high concentration of LA was generated under hypoxia; it could promote tumor progression and metastasis with the involvement of macrophages. The inhibition of LA release impaired this protumor phenomenon. Mechanically, LA induced M2 macrophages through the AKT/ERK signaling pathway; subsequently, M2 macrophages secreted CCL8 and facilitated the proliferation and metastasis of CRC cells by activating the CCL8/CCR5/mTORC1 axis. This effect was inhibited by the antagonist or knockdown of CCR5. In conclusion, lactate-induced CCL8 in TAMs accelerated CRC proliferation and metastasis through the CCL8/CCR5/mTORC1 axis.

As an RNA-binding protein, insulin-like growth factor 2 mRNA-binding protein 2 (IGF2BP2) is involved in enhancing the progression of a few malignant tumors by recognizing N6-methyladenosine on targeted RNA. However, the specific effects of IGF2BP2 on gastric cancer (GC) and the underlying mechanisms remain unclear. In this study, the expression level of IGF2BP2 was evaluated by analyzing data from a public database and performing immunohistochemical staining with GC specimens. The effect of IGF2BP2 on GC cell metastasis was investigated by Transwell assays and animal studies. RNA immunoprecipitation (RIP) was performed to identify potential mRNA bound to IGF2BP2. The levels of these identified RNAs were measured by RT-PCR, while corresponding proteins were quantified via Western blot. It was revealed that IGF2BP2 expression in GC tissues was significantly upregulated, and its overexpression was significantly associated with worse survival in GC patients. The aberrant expression of IGF2BP2 was demonstrated to promote the invasion and metastasis of GC cells by both in vivo and in vitro experiments. In subsequent experiments, it was then verified that by directly interacting with HMGA1 mRNA, IGF2BP2 augmented its stability and thus increased its expression. The knocking down of IGF2BP2 could significantly decrease the migration and invasion of GC cells, which could be reversed by increasing HMGA1 expression. Additionally, both in vitro and in vivo epithelial-mesenchymal transition (EMT) of GC cells were enhanced by IGF2BP2/HMGA1 axis. In conclusion, it was proven in our study that the IGF2BP2/HMGA1/EMT axis contributed to GC metastasis, suggesting its potential as a novel predictive and therapeutic biomarker for GC.

Syntaxin-6 (STX6), a vesicular transport protein, is a direct target of the tumor suppressor gene P53, supporting cancer growth dependent on P53. However, STX6's function in the tumor microenvironment has yet to be reported. In this research, we comprehensively explored the role of the oncogene STX6 in pan-cancer by combining data from several databases, including the Cancer Genome Atlas, CPTAC, cBioPortal, and TIMER. Then, we verified the carcinogenic effect of STX6 in hepatocellular carcinoma (HCC) and colorectal cancer (CRC) through a series of experiments in vitro and in vivo. Bioinformatics analysis demonstrated that STX6 is an oncogene for several cancers and is mainly involved in the cell cycle, epithelial-mesenchymal transition, oxidative phosphorylation, and tumor immune modulation, especially for tumor-associated fibroblasts (CAFs) and NKT cells. Additionally, a high level of STX6 could indicate patients' resistance to immunotherapy. Our own data indicated that the STX6 level was upregulated in HCC and CRC. Knockdown of the STX6 levels could arrest the cell cycle and restrain cell proliferation, migration, and invasion. RNA-seq indicated that STX6 was significantly involved in pathways for cancer, such as the MAPK signal pathway. In a mouse model, knockdown of STX6 inhibited tumor growth and potentiated anti-PD-1 efficacy. In light of the essential roles STX6 plays in carcinogenesis and cancer immunology, it has the potential to be a predictive biomarker and a target for cancer immunotherapy.