Enterococcus faecalis Promotes Chemoresistance in Colorectal Cancer via Lactate-Mediated MOB3B Down-Regulation

Abstract

AIM: To investigate the role of Enterococcus faecalis (E. faecalis) in colorectal cancer (CRC) chemoresistance and elucidate the underlying molecular mechanisms. METHODS: Conditioned media (CM) were collected from cultures of E. faecalis treated with oxaliplatin or 5-fluorouracil (5-FU). The effects of these media on CRC chemoresistance were evaluated using in vitro functional assays and in vivo xenograft models in nude mice. Bioinformatics analysis was conducted to identify candidate genes associated with E. faecalis-induced chemoresistance. Gain- and loss-of-function experiments were performed to assess the role of MOB3B in regulating CRC cell proliferation and drug sensitivity. RT-qPCR, Western blot, and immunohistochemistry were used to validate the molecular mechanisms involved. Metabolomic profiling identified key metabolites in E. faecalis-oxaliplatin CM, and their roles in drug resistance were also confirmed. RESULTS: Compared with oxaliplatin treatment alone, E. faecalis-oxaliplatin CM significantly promoted CRC cell growth and chemoresistance in vitro (P<0.01). Tumors treated with E. faecalis-oxaliplatin CM exhibited significantly larger volumes and faster growth in vivo (P<0.01). Mechanistically, down-regulation of MOB3B mediated the chemoresistance-promoting effects of E. faecalis-oxaliplatin CM (P<0.01). Overexpression of MOB3B inhibited CRC cell proliferation and enhanced chemosensitivity, whereas MOB3B knockdown produced the opposite effect (P<0.01). Metabolomic analysis revealed elevated lactate levels in the E. faecalis-oxaliplatin CM (P<0.01). Lactate inhibition significantly reduced CRC cell proliferation, reversed chemoresistance, and restored MOB3B expression (P<0.01). CONCLUSION: E. faecalis promotes chemoresistance in CRC through lactate-mediated down-regulation of MOB3B, highlighting MOB3B as a potential therapeutic target for overcoming CRC chemoresistance.

1. Introduction

Colorectal cancer (CRC) ranks as the third most commonly diagnosed cancer and the second leading cause of cancer-related death worldwide, posing a significant global health burden. More than 80% of CRC cases are diagnosed at an advanced stage due to the absence of early symptoms. Notably, distant metastases occur in approximately 20% of CRC patients at the time of initial diagnosis. Over the past century, surgery has remained the major treatment for CRC, although the five-year survival rate consistently hovers around 50%. Postoperative chemotherapy is the standard treatment, particularly for CRC patients with inoperable or advanced-stage disease. Moreover, neoadjuvant chemoradiotherapy, total mesorectal excision and adjuvant chemotherapy are current standard treatment options for patients with locally advanced rectal adenocarcinoma. Although most patients initially respond to combination chemotherapy regimens, the emergence of drug resistance often leads to tumor recurrence, resulting in a five-year survival rate of less than 10%. Therefore, elucidating the mechanisms underlying CRC chemoresistance is of critical importance for improving therapeutic outcomes.

In recent years, aberrant gut microbiota has been increasingly recognized as an important modulator of CRC occurrence, progression, and chemotherapy sensitivity. With the deepening understanding of host-microbe interactions, the concept of intratumoral microbiota has emerged, referring to microbial communities residing within tumor tissues. Intratumoral microbiota can modulate tumor progression and drug sensitivity by inducing DNA damage, activating oncogenic pathways, promoting immunosuppression, and metabolizing therapeutic agents. Notably, the gut microbiota plays a crucial role in drug metabolism. Alterations in the gut microbial community contribute to individual variations in drug responses, including drug-induced toxicity and therapeutic efficacy. Studies have shown that γ-proteobacteria can metabolize the chemotherapeutic agent gemcitabine (2',2'-difluorodeoxycytidine) into its inactive form, 2',2'-difluorodeoxyuridine, through the action of bacterial enzyme cytidine deaminase. Moreover, accumulating evidence indicates that certain gut bacteria can also metabolize or modulate the efficacy of oxaliplatin, a first-line chemotherapeutic agent for CRC. Furthermore, studies have demonstrated that the microbial community within tumors, such as Fusobacterium nucleatum, can promote chemotherapy resistance by altering the host's metabolic state rather than directly degrading drugs, highlighting the complexity of the "bacteria-host" interaction at the metabolic level.