Rapamycin Signalling Profile on THP-1

Key Takeaways

• Rapamycin upregulates PI3K regulatory subunit PIK3R1 (+1.20) as feedback.
• ERK immediate‑early genes FOS, EGR1, MYC surge despite stable MAPK kinases.
• Autophagy genes ATG7 rise while ULK1 and LC3B mRNA fall.
• Innate cytokines CCL2, TNF, MX1 strongly induced, revealing inflammatory signature.
• Metabolic HIF targets GLUT1, LDHA, VEGFA suppressed, indicating Warburg shutdown.

Pulse Analysis

Rapamycin’s classic reputation as an mTORC1 inhibitor masks a broader transcriptional impact that becomes evident in THP‑1 monocytes. By releasing negative feedback on the PI3K/AKT pathway, cells attempt to restore growth signaling, as shown by the up‑regulation of PIK3R1, AKT1/3 and mTORC1 scaffolding components. This compensatory loop is a hallmark of resistance to mTOR‑targeted therapies and underscores why monotherapy often fails in aggressive leukemias. Understanding these feedback dynamics helps researchers design rational combinations, such as pairing rapamycin with PI3K inhibitors to blunt the rebound effect.

Beyond metabolic suppression, rapamycin provokes a striking transcriptional activation of immediate‑early genes downstream of ERK, including FOS, EGR1 and MYC, even though MAPK1/3 protein levels remain largely unchanged. This suggests that mTORC1 blockade redirects signaling flux toward the RAS/ERK axis, a well‑documented bypass that fuels cell survival and proliferation. Clinically, the phenomenon explains why patients receiving rapamycin analogs may exhibit limited efficacy unless ERK pathway inhibitors are co‑administered, a strategy currently explored in solid‑tumor trials.

Perhaps most paradoxical is the simultaneous induction of innate immune mediators—CCL2, TNF, MX1, ISG15—while adaptive immunity is suppressed. This rapamycin‑induced inflammatory signature mirrors observations in transplant patients who develop cytokine‑driven complications despite immunosuppression. The down‑regulation of HIF‑controlled metabolic genes further reprograms THP‑1 cells away from aerobic glycolysis, positioning rapamycin as a metabolic re‑setter. Together, these layers of signaling cross‑talk provide a nuanced view of rapamycin’s actions, guiding more precise therapeutic regimens that anticipate and counteract its compensatory pathways.