Honglin Luo

 
Prospective Graduate Students / Postdocs

This faculty member is currently not actively recruiting graduate students or Postdoctoral Fellows, but might consider co-supervision together with another faculty member.

Professor

Research Classification

Viral Infections
Cardiomyopathy
Lung Cancer
Central Nervous System Inflammatory Diseases

Research Interests

Protein quality control in cardiac remodeling
Oncolytic virus for lung cancer therapy
Enteroviral infection and neurodegeneration

Relevant Degree Programs

 

Research Methodology

Viral myocarditis mouse model
SOD1-mutant ALS mouse model
Lung cancer mouse model
Virological techniques
Proteasome and Autophagy study-related technology

Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - May 2019)
The development of coxsackievirus type B3 as a novel oncolytic virus against KRAS-mutant non-small-cell lung cancer (2018)

Lung cancer is the leading cause of cancer-related deaths worldwide. Despite a better understanding of the molecular mechanisms of lung cancer and the subsequent emergence of targeted therapies, treatment responses are typically short-lived. Oncolytic virotherapy provides a possible alternative direction for controlling this incurable disease. Coxsackievirus type B3 (CVB3) is a common human pathogen associated with viral myocarditis in young adults. Due to its highly lytic nature and ability to selectively replicate within cancerous cells, I hypothesize that CVB3 can be developed as an oncolytic virus. Here we demonstrated that in vitro, CVB3 specifically targets KRAS-mutant (KRASmut) non-small-cell lung cancer (NSCLC), a subtype of NSCLC with limited treatment options. Furthermore, we showed in vivo that intratumoral injection of CVB3 significantly reduces tumor volumes in patient-derived KRASmut NSCLC xenograft models. Mechanistically, we found that aberrant activation of the extracellular signal-regulated kinase 1/2 (ERK1/2) signaling and elevated expression of the coxsackievirus and adenovirus receptor (CAR), the primary receptor for CVB3 internalization, are associated with preferential replication of CVB3 within KRASmut NSCLC. However, despite a satisfactory tumor regression rate, CVB3 treatment leads to the onset of viral myocarditis in immunocompromised mouse models, indicating that potential safety issues need to be addressed prior to its potential application in lung cancer therapy. It is known that CVB3 subverts host machinery to gain survival advantages, and this process is highly associated with a spectrum of human disorders. We reported that Grb2-associated binding protein 1 (GAB1), a scaffolding adaptor protein responsible for intracellular signaling assembly and transduction, plays a crucial role in regulating compensatory cardiac response to aging and hemodynamic stress. Furthermore, we demonstrated that both GAB1 and Grb2-associated binding protein 2 (GAB2, a functional homologue of GAB1), are proteolytically cleaved after CVB3 infection by virus-encoded protease 2Apro, independent of caspase activation. We showed that virus-induced cleavage of GAB1 is beneficial for viral growth as the resulting cleavage fragment (GAB1-N₁₋₁₇₄) further enhances ERK1/2 activation and promotes viral replication. Taken together, our findings suggest that CVB3 is a potent oncolytic agent against KRASmut NSCLC, and that elimination of CVB3-induced cardiotoxicity would significantly enhance the safety of this virotherapy.

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Interplay between stress granules, cellular stress response, and coxsackievirus B3 infection (2016)

Viral infection affects a multitude of cellular processes to facilitate successful replication. Such responses include the formation of stress granules (SGs) and the activation of autophagy. SGs are stalled translational complexes and function to restore cellular homeostasis after stress. Autophagy is a cellular process that recycles misfolded proteins and damaged organelles and plays an important role in various stress responses. We previously demonstrated that infection with Coxsackievirus B3 (CVB3), a common human pathogen for viral myocarditis, disrupts the autophagic process to support effective viral replication. However, the interplay between CVB3 and SGs, and the ability of SGs to regulate autophagy have not been investigated. Here we showed that SGs are formed early and actively disassembled late during CVB3 infection due to viral protease 3Cpro-mediated cleavage of Ras-GAP SH3 domain binding protein 1 (G3BP1), a key nucleating protein of SGs. Overexpression of G3BP1 inhibits CVB3 replication, indicating an anti-viral function of SGs. We further demonstrated that the C-terminal product of G3BP1 has a toxic gain-of-function that further inhibits SG formation. We also examined the interaction between CVB3 and the transactive response DNA-binding protein-43 (TDP-43), an RNA binding protein that mislocates to SGs under cellular stress. We found that TDP-43 is translocated from the nucleus to SGs upon infection through the activity of viral protease 2Apro, followed by cleavage by protease 3Cpro. The C-terminal product of TDP-43 is quickly degraded by the proteasome, whereas the N-terminal truncate acts as a dominant-negative mutant that inhibits the function of native TDP-43 in alternative RNA splicing. Knockdown of TDP-43 results in an increase in viral titres, suggesting a protective role for TDP-43 in CVB3 infection. Lastly, we explored the possible role of G3BP1-SGs in regulating autophagy. We showed that G3BP1 inhibits autophagic flux, likely by binding to cytoplasmic signal transducer and activator of transcription 3 (STAT3). Taken together, our results reveal that the host SGs and associated proteins, including G3BP1 and TDP-43, are utilized and modified during CVB3 infection to promote efficient viral replication and induce viral pathogenesis. Moreover, we propose a novel mechanism by which G3BP1 binds cytoplasmic STAT3 to inhibit autophagy.

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Disruption of selective autophagy in coxsackievirus B3 infection (2015)

Coxsackievirus infection induces an abnormal accumulation of ubiquitin aggregates that are generally believed to be harmful to the cells and play a key role in the pathogenesis of coxsackievirus-induced myocarditis and dilated cardiomyopathy. Selective autophagy mediated by autophagy adaptor proteins, including sequestosome 1 (SQSTM1/p62) and neighbor of BRCA1 gene 1 protein (NBR1), is an important pathway for disposing of misfolded proteins and damaged organelles. We demonstrated that SQSTM1 was cleaved following CVB3 infection through the proteolytic activity of viral proteinase 2Apro. The resulting cleavage fragments of SQSTM1 were no longer the substrates of autophagy, and their ability to form protein aggregates was greatly decreased due to incapability of interaction with ubiquitinated proteins. We further tested whether NBR1, a functional homolog of SQSTM1, can compensate for SQSTM1 loss-of-function after viral infection. Of interest, we found that NBR1 was also cleaved after coxsackievirus infection, excluding the possible compensation of NBR1 for the loss of SQSTM1. This cleavage took place at two sites mediated by virus-encoded proteinase 2Apro and 3Cpro, respectively. In addition to the loss-of-function, we showed that the C-terminal fragments of SQSTM1 and NBR1 exhibited a dominant-negative effect against native SQSTM1/NBR1, probably by competing for LC3 and ubiquitin chain binding. Apart from the disruption of selective autophagy, CVB3 infection also impaired autophagic flux as confirmed by flux assays with a combination of a tandem fluorescence-tagged LC3 stable cell line and a non-cleavable construct of SQSTM1. Finally, we studied the roles of SQSTM1 and NBR1 in autophagic degradation of depolarized mitochondria (referred to as mitophagy). Following mitochondrial depolarization induced by carbonyl cyanide m-chlorophenylhydrazone (CCCP), a mitochondrial uncoupler to trigger mitophagy, we demonstrated that NBR1 did not appear to be required for mitochondrial clustering. Deficiency of NBR1 alone or in concert with SQSTM1 did not block the clearance of damaged mitochondria, suggesting that NBR1 is dispensable for mitophagy regardless of the status of SQSTM1. Taken together, the findings in this study suggest novel mechanisms in coxsackieviral pathogenesis: coxsackievirus infection induces abnormal accumulation of ubiquitin conjugates through the disruption of selective degradation of protein aggregates and blockage of autophagic flux.

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Host protein manipulation as a mechanism in viral cardiomyopathy (2012)

Viral myocarditis, the inflammation of myocardium initiated by viral infection, is an important cause of mortality in neonates and children. In addition, it is a precursor to dilated cardiomyopathy (DCM). To date, no effective therapy is available for viral myocarditis/DCM. Coxsackievirus B3 (CVB3) is an important human pathogen of viral myocarditis. Extensive research efforts on CVB3 have broadened our understanding of the virus-host protein interactions. However, the pathogenesis of coxsackievirus-induced myocarditis is not fully understood. The objective of this dissertation is to explore the role of host protein manipulation in coxsackieviral replication and pathogenicity. My hypotheses are that (1) coxsackievirus hijacks host’s cellular autophagy mechanism to facilitate its own replication; and (2) the serum response factor (SRF) is cleaved by viral protease 2A during coxsackievirus infection and contributes to impaired myocardial function and progression to DCM. For project 1, I demonstrated that CVB3 manipulates the host autophagy pathway to supplement viral replication. Autophagy is an evolutionary conserved homeostatic mechanism in eukaryotes that degrades and recycles long-lived cytoplasmic proteins, as well as damaged organelles. The hallmark of autophagy is the formation of double-membrane vesicles known as autophagosomes. I provided the initial evidence that CVB3 infection induces the formation of autophagosomes. Up-regulation of autophagosome formation enhances CVB3 replication, whereas downregulation of autophagy pathway reduces CVB3 replication. My results help clarify the nature of the intracellular membranes previously shown to be required for viral replication. For project 2, I demonstrated that CVB3 manipulates SRF expression via protein cleavage. SRF is a transcription factor vital for the expression of cardiac contractile/regulator genes, as well as gene silencing microRNAs. Cardiac-specific knockout of SRF in adult transgenic mice results in disruption of cardiac gene expression and development of severe DCM. I showed that SRF is cleaved in CVB3-infected mouse hearts and cardiomyocytes. Further studies revealed that SRF is cleaved at the 327 amino acids position by CVB3-encoded protease 2A. I demonstrated that SRF cleavage contributes to DCM by abolishing the transactivation property of SRF and generating dominant-negative SRF-truncates. Taken together, these novel viral strategies bridged existing knowledge and may serve as therapeutic targets for viral myocarditis/DCM.

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