CML-076 The Downregulation of Both Large E3 Ubiquitin Ligases, HERC1 and HERC2, is a Common and Unambiguous Feature of Chronic Myeloid Leukemia

• Published in: Clinical lymphoma, myeloma and leukemia myeloma and leukemia, 2023-09, Vol.23, p.S332-S333
• Main Authors: Ali, Muhammad Shahzad, Munir, Zunaira, Panuzzo, Cristina, Ashraf, Nabeel, Magnati, Stefano, Pergolizzi, Barbara, Bracco, Enrico, Saglio, Giuseppe
• Format: Article
• Language: English
• Subjects: CML; differentiation; large HERCs; TKIs; ubiquitin proteasome system
• ISSN: 2152-2650; 2152-2669
• DOI: 10.1016/S2152-2650(23)01123-0

Protein degradation by the ubiquitin-proteasome system (UPS) has been shown to regulate hematopoietic stem cell (HSC) self-renewal, differentiation, and survival. The balance between HSC self-renewal and differentiation is critical to maintaining hematopoiesis and its dysregulation is often associated with malignancies, including chronic myeloid leukemia (CML). Large HERC E3 ligase family members, HERC1 and HERC2, are staggeringly complex proteins that can intervene in a wide range of physiological processes, such as cell proliferation, DNA repair, neurodevelopment, and inflammation. Therefore, mutations or dysregulation of large HERCs are associated with neurological disorders, DNA repair defects, and cancer. Their roles in non-solid neoplasms remain unknown. Hence, in the present study, we explored the roles of the large HERCs in CML. After written informed consent, blood specimens from patients with CML were collected at diagnosis, remission, and relapse alongside healthy subjects. RT-PCR was used to screen all patients for the presence of the BCR-ABL fusion gene. Differentiation was performed by incubating myeloid leukemia cell lines (i.e., HL60, NB4, and K562) with PMA and ATRA. HERCs mRNA quantification was done by RT-qPCR. Immunofluorescence and western blots were performed to assess the protein expression. Flow cytometry was used to assess cell surface differentiation markers. Both HERCs were down-modulated at CML onset, with a tight and unambiguous inverse correlation between the presence of the fusion oncogene BCR-ABL1. Upon remission, both HERC1 and HERC2 mRNAs return to levels comparable to those of their healthy counterparts. Additionally, our survey unveils that their gene expression is sensitive to different tyrosine kinase inhibitors (TKIs) in a time-dependent fashion. Interestingly, HERC1 protein physically interacted with BCR-ABL1. A differential HERC1 expression was also observed when the leukemic cell lines were induced to differentiate towards different lineages. These findings let us surmise both giant HERCs’ putative role in the CML's chronic phase. We also observed that the HERC1 levels were tightly linked to cell fate. Remarkably, our findings suggest that, at least in blood cells, HERC1 might be a novel differentiation marker.