Autophagy has the functions of maintaining intracellular homeostasis, regulating cellular differentiation and responding to external cellular stress. CMA is implicated in many bio-processes, including transcriptional regulation, DNA replication, and immune response regulation. In particular, numerous investigations have reported that CMA often plays a pro-cancer function in tumor progression (Kaushik and Cuervo 2018). The reason for this may be due to two points; on the one hand, CMA-degrading proteins can provide tumor cells with the energy they need for growth. On the other hand, CMA-degrading proteins can provide raw materials for biosynthesis in tumor cells (Zhou et al. 2016, Xie et al. 2015). There is a rate-limiting step in CMA where the substrate binds to LAMP2A (Cuervo and Dice 2000). The expression and activity of LAMP2A directly affects the activity of CMA, and thus targeting LAMP2A may enable the targeting of CMA in the clinic.
It has been documented that LAMP2A is highly exhibited in a number of malignant tumors, such as HCC cells, lung cancer cells, gastric cancer cells, and cervical cancer cells (Kon et al. 2011). For example, it was found that high LAMP2A in breast cancer contributed to poor prognosis and increased cancer cell viability in HER2-negative breast cancer patients (Tokarchuk et al. 2021). Similarly, in non-small cell lung cancer, elevated LAMP2A expression was also observed, which contributed to the poor prognosis of patients and cisplatin resistance development. In contrast, knockdown of LAMP2A expression improved therapeutic properties and sensitivity to cisplatin treatment in mice (Ichikawa et al. 2020). In addition, it has been reported that upregulated LAMP2A-mediated hyperactivation of CMA in human grade IV glioblastoma regulates malignant progression of tumor cells by targeting SMAD3 degradation (Liu et al. 2022). Upregulation of LAMP2A expression also regulates apoptosis and proliferation of CRC cells (Peng et al. 2020). However, there are still few studies on LAMP2A in CRC progression, especially reports related to chemoresistance. Only one report was found that high LAMP2A led to 5-FU resistance and enhanced PLD2 through NF-κB pathway activation, thereby promoting the proliferation, invasion, and anti-apoptotic functions of CRC drug-resistant cells (Xuan et al. 2021). Therefore, more investigations are required to reveal the influence and mechanism of LAMP2A on CRC resistant to different chemotherapeutic agents. Consistent with the above reports, LAMP2A expression was also enhanced in CRC tissues, and high levels of LAMP2A were linked to poor prognosis in CRC. In addition, we found that LAMP2A was obviously augmented in DDP-resistant CRC as well, suggesting that LAMP2A may be associated with DDP-resistant progression in CRC. In addition, LAMP2A overexpression heightened CRC/DDP proliferation, migration, invasive ability and DDP resistance. In contrast, LAMP2A knockdown lightened the malignant progression of CRC/DDP and increased cell sensitivity to DDP.
Cisplatin is one of the platinum-based chemotherapeutic agents used to treat various types of cancer (Song, Cui and Liu 2022, Shen et al. 2022). During cisplatin chemotherapy, the drug forms a complex with deoxyribonucleic acid (DNA), which inhibits the formation of ribonucleic acid from DNA and thus induces apoptosis (Dasari and Tchounwou 2014). Although the majority of patients have a good initial response to cisplatin, most patients eventually relapse and progress. This is due to the development of resistance to cisplatin in this group of patients (Wang et al. 2021). This resistance constrains the prognosis of CRC patients and makes the cancer progress in a bad direction (Makovec 2019). Therefore, it is important to explore the mechanism of cisplatin resistance in CRC to improve the treatment of CRC patients. More and more studies have shown that autophagy is closely related to chemotherapy resistance. Autophagy plays a dual role in the progression of drug resistance in cancer (Sui et al. 2013). Several reports have confirmed that various antitumor agents induce autophagic death of cancer cells (Liu et al. 2017). However, there is also evidence that autophagy contributes to chemotherapy resistance in various types of cancer (Luo et al. 2021). In addition, autophagy is often accompanied by changes in associated marker proteins. p62 is involved in intracellular signaling and regulation of autophagy, which in turn maintains cellular homeostasis (Vargas et al. 2023). Impaired or inhibited cellular autophagy leads to the accumulation of p62, which in turn activates intracellular signaling pathways associated with the p62 protein (Lamark, Svenning and Johansen 2017). Furthermore, LC3 protein is another signature protein associated with autophagy.LC3II expression shows a positive correlation with autophagic activity (Peña-Martinez, Rickman and Heckmann 2022). LC3II protein induces the fusion of autophagosomes with lysosomes to accomplish the degradation of damaged mitochondria (Heckmann and Green 2019). In addition, LC3II is converted from LC3Ⅰ, so an increase in LC3II is often accompanied by a decrease in LC3Ⅰ (Mizushima and Yoshimori 2007). Therefore, LC3II/LC3Ⅰ is also used as an indicator to characterize autophagic activity. We found that when intracellular LAMP2A was enhanced, p62 was limited, and the ratio of LC3II/LC3Ⅰ was enhanced, which indicated that autophagy was strengthened in cells. In contrast, when the intracellular LAMP2A was attenuated, the accumulation of p62 was induced, while the ratio of LC3II/LC3Ⅰ was restrained, which indicated that autophagy was weakened in the cell. This revealed that LAMP2A motivated the proliferation, migration, invasion and cisplatin resistance of CRC/DDP cells by mediating autophagy. Finally, in vivo experiments also confirmed that knockdown of LAMP2A limited tumor formation and boosted the sensitivity of the organism to DDP.
In conclusion, this study established that LAMP2A mediated cisplatin resistance in CRC by stimulating autophagy. However, there are still many questions to be solved and refined in our study. For example, does LAMP2A also affect chemoresistance in CRC through other signaling pathways, and is LAMP2A also involved in the regulation of CMA autophagy? In addition, the upstream and downstream regulatory mechanisms by which LAMP2A affects autophagy still need to be further investigated. These queries will continue to be investigated in depth in future studies, and in the meantime, we also hope that our study can provide possible targets for clinical treatment to overcome CRC drug resistance.