Asst. Prof. Dr. Umut ŞAHIN

Boğaziçi University
Molecular Biology and Genetics
Kuzey Park, 312
34342 Bebek - Istanbul
+90 (212) 359 7383
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My group studies the basic science and medical aspects of a vital eukaryotic process called sumoylation, and of the tightly-linked PML protein, a prominent tumor suppressor.

Small Ubiquitin-like Modifiers

Sumoylation is a post-translational protein modification essential for life, which involves covalent conjugation of target proteins with the SUMO (small ubiquitin-like modifier) peptide. This may alter target function, enzymatic activity, subcellular localization and stability. Sumoylation also regulates macromolecular interactions, aggregation and solubility. One of the major interests of my group is to explore potential implications of the latter for the pathogenesis and management of neurodegenerative diseases. An unexpected consequence of sumoylation has recently emerged: sumoylation of a target may also trigger its ubiquitination and destruction by the proteasome.

Nuclear Organization & PML Nuclear Bodies

Aside from harboring a vast amount of genetic material, the eukaryotic nucleus is highly organized into distinct microenvironments such as PML nuclear bodies. This organization is often compromised in cancer and viral diseases. For example, in acute promyelocytic leukemia (APL), an aggressive subtype of myeloid leukemias, PML nuclear bodies are disrupted. A combination of two potent drugs - arsenic & retinoic acid - can enforce reformation of PML nuclear bodies and cure APL. The scaffold of PML nuclear bodies is the PML (promyelocytic leukemia) protein. In APL a genetic defect creates a fusion oncogene: PML/RARA. The latter impairs the function of PML protein and disrupts PML nuclear bodies. PML nuclear bodies recruit numerous partner proteins, including transcription factors (i.e. P53, Rb) and DNA repair proteins.

As a post-doc in Hugues de Thé’s lab, together with Valérie Lallemand-Breitenbach, I have recently identified the long-sought biochemical function of PML nuclear bodies as catalytic drivers of partner protein sumoylation and/or ubiquitination & degradation. We have demonstrated that some toxic proteins can be pharmacologically forced and channelled into this “PML/SUMO/Ubiquitin-mediated degradation” system (i.e. HTLV1 Tax oncoprotein) with a clear clinical benefit in leukaemia patients.

Selected Publications

  • PML nuclear bodies: assembly and oxidative-stress sensitive sumoylation (2014) Nucleus. Sahin U et al.

  • PML nuclear bodies: regulation, function and therapeutic perspectives (2014) J Pathol. Sahin U et al.

  • Oxidative stress-induced assembly of PML nuclear bodies controls sumoylation of partner proteins (2014) J Cell Biol. Sahin U et al.

  • Interferon controls SUMO availability via the Lin28 and let-7 axis to impede virus replication (2014) Nat Commun. Sahin U et al.

  • Adult T-cell lymphoma response to arsenic/interferon therapy is triggered by SUMO/PML/RNF4-dependent Tax degradation (2015) Blood. Sahin U/Dassouki Z et al.