PDCD4 as a marker of mTOR pathway activation and therapeutic target in mycobacterial infections

ABSTRACT Programmed cell death protein 4 (PDCD4) is instrumental in regulating a range of cellular processes such as translation, apoptosis, signal transduction, and inflammatory responses. There is a notable inverse correlation between PDCD4 and the mammalian target of rapamycin (mTOR) pathway, which is integral to cellular growth control. Activation of mTOR is associated with the degradation of PDCD4. Although the role of PDCD4 is well established in oncogenesis and immune response regulation, its function in mycobacterial infections and its interplay with the mTOR pathway necessitate further elucidation. This study investigates the modulation of PDCD4 expression in the context of mycobacterial infections, revealing a consistent pattern of downregulation across diverse mycobacterial species. This observation underscores the potential utility of PDCD4 as a biomarker for assessing mTOR pathway activation during such infections. Building on this finding, we employed a novel approach using PDCD4-based mTOR (Tor)-signal-indicator (TOSI) reporter cells for the high-throughput screening of FDA-approved drugs, focusing on mTOR inhibitors. This methodology facilitated the identification of several agents, inclusive of known mTOR inhibitors, which upregulated PDCD4 expression and concurrently exhibited efficacy in impeding mycobacterial proliferation within macrophages. These results not only reinforce the significance of PDCD4 as a pivotal marker in the understanding of infectious diseases, particularly mycobacterial infections, but also illuminate its potential in the identification of mTOR inhibitors, thereby contributing to the advancement of therapeutic strategies. IMPORTANCE This study emphasizes the critical role of the mammalian target of rapamycin (mTOR) pathway in macrophage responses to mycobacterial infections, elucidating how mycobacteria activate mTOR, resulting in PDCD4 degradation. The utilization of the (Tor)-signal-indicator (TOSI) vector for real-time monitoring of mTOR activity represents a significant advancement in understanding mTOR regulation during mycobacterial infection. These findings deepen our comprehension of mycobacteria's innate immune mechanisms and introduce PDCD4 as a novel marker for mTOR activity in infectious diseases. Importantly, this research laid the groundwork for high-throughput screening of mTOR inhibitors using FDA-approved drugs, offering the potential for repurposing treatments against mycobacterial infections. The identification of drugs that inhibit mTOR activation opens new avenues for host-directed therapies, marking a significant step forward in combating tuberculosis and other mycobacterial diseases.