Smad Ubiquitination Regulatory Factor 1 (Smurf1) Promotes Thyroid Cancer Cell Proliferation and Migration via Ubiquitin-Dependent Degradation of Kisspeptin-1

BACKGROUND/AIMS

Thyroid cancer is the most common malignancy in human endocrine system. Smad ubiquitination regulatory factor 1 (Smurf1) is an E3 ubiquitin-protein ligase in ubiquitin-proteasome pathway (UPP) system. This study aimed to investigate the effects of Smurf1 on thyroid cancer proliferation and metastasis, as well as underlying potential mechanism.

METHODS

The expression levels of Smurf1 in thyroid tumor tissues and thyroid cancer cells were detected by western blotting and qRT-PCR. Then, the effects of up-regulation or down-regulation of Smurf1 on thyroid cancer cell viability, migration, invasion, proliferation and apoptosis were measured using trypan blue exclusion assay, two-chamber migration (invasion) assay, cell colony formation assay and Guava Nexin assay, respectively. The ubiquitination of kisspeptin-1 (KISS-1) was assessed by protein ubiquitination assay. Finally, the effects of KISS-1 overexpression on activity of nuclear factor-kappa B (NF-κB) signaling pathway, as well as thyroid cancer cell viability, migration, invasion, proliferation and apoptosis were also detected, respectively.

RESULTS

Smurf1 was highly expressed in thyroid tumor tissues and thyroid cancer cells. Up-regulation of Smurf1 promoted the viability, migration, invasion and proliferation of thyroid cancer cells. Knockdown of Smurf1 had opposite effects. Moreover, smurf1 promoted the ubiquitination of KISS-1. Overexpression of KISS-1 inactivated NF-κB pathway, suppressed thyroid cancer cell viability, migration, invasion and proliferation, and induced cell apoptosis.

CONCLUSION

Up-regulation of Smurf1 exerted important roles in thyroid cancer formation and development by promoting thyroid cancer proliferation and metastasis. The ubiquitin-dependent degradation of KISS-1 induced by Smurf1 and the activation of NF-κB signaling pathway might be involved in this process. Smurf1 could be an effective therapy target and biomarker for thyroid cancer treatment.

The Role of Smurf1 in Neuronal Necroptosis after Lipopolysaccharide-Induced Neuroinflammation

The role of inflammation in neurological disorders such as Alzheimer's disease and Parkinson's disease is gradually recognized and leads to an urgent challenge. Smad ubiquitination regulatory factor 1 (Smurf1), one member of the HECT family, is up-regulated by proinflammatory cytokines and associated with apoptosis in acute spinal cord injury. However, the function of Smurf1 through promoting neuronal necroptosis is still limited in the central nervous system (CNS). Hence, we developed a neuroinflammatory model in adult rats following lipopolysaccharide (LPS) lateral ventral injection to elaborate whether Smurf1 is involved in necroptosis in CNS injury. The up-regulation of Smurf1 detected in the rat brain cortex was similar to the necroptotic marker RIP1 expression in a time-dependent manner after LPS-induced neuroinflammation. Meanwhile, Smurf1 knockdown with siRNA inhibited neuronal necroptosis following LPS-stimulated rat pheochromocytomal PC12 cells. Thus, it was indicated that LPS-induced necroptosis could be promoted by Smurf1. In short, these studies suggest that Smurf1 might promote neuronal necroptosis after LPS-induced neuroinflammation, which might act as a novel and potential molecular target for the treatment of neuroinflammation associated diseases.

Immunolocalization of Smurf1 in Hirano bodies

The Smad ubiquitination regulatory factor 1 (Smurf1) is one of the E3 ubiquitin ligases and is related to multiple biological processes. Despite the various roles played by this protein, there is no report on the function of Smurf1 in neurodegeneration. Hirano bodies (HBs) are intracellular structures within neuronal processes and were first described in the hippocampus of individuals with amyotrophic lateral sclerosis and the parkinsonism-dementia complex of Guam. In addition, the number of HBs increases in the brains of patients with Alzheimer's disease (AD) compared with age-matched non-demented control individuals. In this study, we immunohistochemically demonstrated that Smurf1 localized in HBs in the brains of patients with AD by using plural anti-Smurf1 antibodies, and Smurf1 co-localized with HBs marker proteins by using confocal microscopy. Moreover, we demonstrated that Smurf1 localized in HB-like F-actin aggregates in a cell culture system via treatment with the actin-stabilizing toxin jasplakinolide (jpk). Smurf1 represents a novel protein component of HBs, to be included in an expanding list of HB-associated proteins.