Thymoquinone suppresses papillary thyroid carcinoma by impairing autophagic flux via the PDZK1IP1/HMGCS1 axis

Background and Aim Thymoquinone (TQ), the principal bioactive constituent of Nigella sativa , has antitumor activity in multiple malignancies, but its mechanism in papillary thyroid carcinoma (PTC) remains incompletely defined. Experimental Procedure We evaluated the effects of TQ on PTC cell proliferation, apoptosis, autophagic flux, and tumor growth, and examined the PDZK1IP1/HMGCS1 axis. Key Results TQ reduced viability and clonogenic growth in TPC-1 and BCPAP cells, increased apoptosis, downregulated PCNA and Bcl-2, and upregulated cleaved caspase-3, cleaved PARP, and BAX. TQ also increased autophagy-related vesicles and p62 and LC3-II levels. Tandem mRFP-GFP-LC3B reporter imaging showed accumulation of both yellow dual-positive and red-only LC3 puncta. Together with pharmacological modulation using bafilomycin A1, chloroquine, and rapamycin, these findings supported impaired late-stage autophagic processing. Integrated public PTC datasets and TQ-treated TPC-1 RNA-seq data identified PDZK1IP1 as a candidate mediator. PDZK1IP1 knockdown enhanced, whereas overexpression attenuated, TQ-induced proliferation inhibition, apoptosis, and autophagy-marker accumulation. HMGCS1 was identified as a downstream effector; its overexpression partially rescued these effects in both TPC-1 and BCPAP cells. In xenografts, TQ suppressed tumor growth, reduced Ki67, PDZK1IP1, and HMGCS1, and increased LC3 and p62. Conclusion and Implications TQ suppresses PTC progression by impairing autophagic flux and downregulating PDZK1IP1/HMGCS1.