Parkin-mediated ubiquitination of hif-α modulates hypoxia signaling in Megalobrama amblycephala.

BACKGROUND: Megalobrama amblycephala is an economically important fish species in Chinese aquaculture, but its high sensitivity to hypoxia poses a major challenge for farming. This study aims to investigate the role of the E3 ubiquitin ligase parkin in regulating hypoxia signaling in fish. RESULTS: Under hypoxic stress, parkin expression was significantly upregulated in oxygen-sensitive tissues (brain and gills) and embryos of M. amblycephala, consistent with the expression of hypoxia-responsive genes. Ma-parkin was found to exhibit high conservation in its key functional domains. Mechanistically, it directly interacts with Ma-hif-α, promoting their ubiquitination and proteasomal degradation via E3 ligase activity, thereby suppressing hif-mediated transcriptional activation. Critical residues T74 and C333 were identified as essential for this activity; mutations at these sites impaired Ma-hif-α degradation and ubiquitination, as well as HRE transactivation. Furthermore, we found that Ma-hif-α can regulate the transcription of parkin, forming a negative feedback loop to fine-tune the hypoxic response. CONCLUSIONS: Our study demonstrates that parkin serves as a key negative regulator of the hypoxia signaling pathway in M. amblycephala, operating through a finely tuned feedback mechanism. The E3 ubiquitin ligase activity of parkin, dependent on critical residues T74 and C333, directly mediates hif-α ubiquitination and degradation. The reciprocal regulation between hif-α and parkin forms a regulatory circuit that modulates the hypoxic response. These findings not only reveal a conserved adaptive mechanism to hypoxia in fish but also identify specific molecular targets for genetic improvement of hypoxia tolerance in aquaculture species.