Current Molecular Medicine - Volume 16, Issue 10, 2016

Sumoylation, a post-translational modification discovered over a decade ago, turns out to be a very important regulatory mechanism mediating multiple cellular processes. Recent studies from our laboratory and others also revealed that it plays a crucial role in regulating both differentiation and pathogenesis of the ocular lens. This review will summarize these progresses.

Sumoylation is a reversible post-translational modification that conjugates small peptide SUMO (small ubiquitin-like modifier) to a target protein. Global protein sumoylation and expression of components in sumoylation pathway were recently found to be altered in the process of organismal aging. In addition, key factors controlling cellular senescence are known to be sumoylated. This review will summarize current information on the function of sumoylation in cellular senescence and aging.

Heart is an extremely important organ, and cardiovascular disorders emerge as primary life-threatening disease in human life. Aberrant post-translational modifications (PTMs) on cardiac proteins are closely correlated with pathological abnormalities in heart. SUMOylation, one of the most prevalent PTMs with thousands of substrates throughout the cell including critical subcellular organelles, has been shown to precisely finetune the cell survival and proliferation during heart development, and delicately control the function of mitochondrion and sarcoplasmic reticulum in physiological heart functioning. The silver lining is pathologically cardiacspecific SUMOylation being considered as target for cardiovascular disease intervention and treatment. Here, we summarize the recent progress in heart-specific functions of the SUMOylation pathway. In particular, we discuss the biological significance of SUMO conjugation/deconjugation during heart development, and in physiological cardiovascular health involving cardiac mitochondrial function, cardiac contractility, stress adaption and protein homeostasis. We also discuss the crosstalks between sumoylation and other post-translational modifications such as acetylation and ubiquitination. These crosstalks not only shed light to our understanding of the regulatory mechanisms on cardiovascular disorders but also contributes to their future therapy.

CREB is an ubiquitous transcription factor regulating diverse cellular responses. Its phosphorylation at S133 is an essential event for its activation in both nervous and visual systems. The activated CREB is implicated in the regulation of development, protection, learning, memory and plasticity in the nerve system. Moreover, sumoylation, an important post-translational modification of protein, plays a key role in sustaining CREB activation in the rat hippocampus in order to enhance the long-term memory and other aspects. In the visual system, although the CREB activation by phosphorylation at S133 is similar to that as observed in the nervous system, the role of CREB sumoylation remains to be explored. This review will discuss the aspects of CREB functions and their regulation by phosphorylation and sumoylation in both systems.

Since the discovery of SUMOs (small ubiquitin-like modifiers) over 20 years ago, sumoylation has recently emerged as an important posttranslational modification involved in almost all aspects of cellular physiology. In neurons, sumoylation dynamically modulates protein function and consequently plays an important role in neuronal maturation, synapse formation and plasticity. Thus, the dysfunction of sumoylation pathway is associated with many different neurological disorders. Hundreds of different proteins implicated in the pathogenesis of neurological disorders are SUMO-modified, indicating the importance of sumoylation involved in the neurological diseases. In this review, we summarize the growing findings on protein sumoylation in neuronal function and dysfunction. It is essential to have a thorough understanding on the mechanism how sumoylation contributes to neurological diseases in developing efficient therapy for these diseases.

Sumoylation is a covalent protein posttranslational modification that conjugates the small ubiquitin-like peptide SUMO to substrate. Sumoylation is critically implicated in multiple biological processes, including cell proliferation, differentiation, senescence and apoptosis, etc. Therefore, it is not surprising that dysregulation of sumoylation has been implicated in tumorigenesis and different types of cancer were found to be addicted to functional sumoylation pathway. The potential role for sumoylation as a therapeutic target in caner is emerging. In this review, we summarize current knowledge regarding the involvement of sumoylation in genome stability and DNA damage response. We will further discuss the therapeutic potential of sumoylation as synthetic lethal partner and as a key signaling pathway in cancer stem cells.

Post-translational modifications (PTMs) such as phosphorylation, acetylation, methylation, ubiquitylation, sumoylation are important mechanisms to regulate functions of different proteins. Among various PTMs, phosphorylation, discovered about 60 years ago, is probably the most common modification. In contrast, sumoylation, identified about two decades ago is emerging as a key regulatory mechanism modulating protein functions. Although studies on protein phosphorylation and sumoylation have been extensively reviewed, much less attention has been paid to their cross-talk and their co-regulation of the same protein target. Here we summarize various examples of the cross-talks between protein phosphorylation and sumoylation, and discuss their functions in regulating normal physiology and pathogenesis.

α-Crystallins, initially identified as the structural proteins of the ocular lens, belong to the small heat shock protein family. They play significant roles in maintaining the lens transparency and preventing protein aggregation. α-Crystallins exist in two isoforms: αA and αB, and they display differential tissue distribution. Their mutations are implicated in several human diseases including cardiac myopathies, neurodegenerative diseases, cataracts and various types of cancers. Increased αB expression was detected in retinoblastoma, breast cancer, glioblastoma, prostate and renal cell carcinomas, indicating its role in promoting tumor growth. A complex picture emerges for αA. Although earlier studies suggest that αA may promote cancer development, recent studies from our laboratory demonstrate that αA can act as a tumor suppressor inhibiting cell transformation and retarding cell migration through modulating MAP kinase activity. In this review, we summarize the recent progress about the functions of αA and αB in cancer development.

Purpose: The protein phosphatase-2A (PP-2A) is one of the most important serine/threonine phosphatases in eukaryotes. The holoenzyme of PP-2A consists of three subunits: a scaffold A subunit, a catalytic C subunit and a regulatory B subunit. While both A and C subunits are coded by two different genes, the B subunits exist in 26 or more isoforms which are encoded by at least 15 different genes. Previous studies have shown that besides regulating specific PP-2A activity, various B subunits may have other functions. To explore the possible roles of the regulatory subunits of PP-2A in vertebrate development, we have cloned the gene encoding goldfish striatin, a member of the B’” family regulatory subunits for PP-2A, and determined their tissue-specific and temporal expression patterns. Methods: The cDNA cloning was conducted with RT-PCR-based RACE. The mRNA expression levels for the goldfish striatin were analyzed with RT-PCR. The expression levels of the striatin protein from goldfish were determined with Western blot analysis. The semi-quantitation of the mRNA and protein expression levels was conducted with the software of U-scanning. Results: Our study revealed that the full length cDNA for striatin consists of 2965 bp coding for a deduced protein of 769 amino acids, which bears a very high level of amino acid sequence identity with the homolog protein from other species. The striatin mRNA is highly expressed in the kidney, to a less degree in brain, fin, muscle, liver, ovary and gill, and the lowest in testis and heart. Similar pattern of protein expression is detected in the above 9 tissues. During the development of goldfish, the striatin mRNA maintains a relatively high level at the 2-cell, multiple cell and blastula stages. Then, it drops down substantially at gastrula stage and fluctuates around this level in the next 8 different stages. At the protein level, the striatin maintained higher level from 2-cell to gastrula stages, then decreased at neurula and optic vesicle stages, and gradually increased again to peak at eye pigmentation stage, then slightly decreased in the next few stages of development. Conclusions: Our results suggest that the striatin may play an important role in regulating goldfish development and adult tissue homeostasis. While the former function may or may not occur through PP- 2A functions, the later function appears to occur via PP-2A activity.