p62 Overexpression Promotes Bone Metastasis of Lung Adenocarcinoma out of LC3-Dependent Autophagy

Abstract

p62 protein has been implicated in bone metastasis and is a multifunctional adaptor protein usually correlated with autophagy. Herein, we investigated p62 expression and its prognostic significance in bone metastasis of lung adenocarcinoma, and analyzed whether the mechanism involved depends on autophagy. mRNA and protein expression of p62, LC3B and Beclin 1 were detected by reverse transcription-quantitative PCR and western blotting, respectively, in fresh bone metastasis tissues (n=6 cases) and normal cancellous bone tissues (n=3 cases). The association between p62 and LC3B expression and patient prognosis was subsequently analyzed in 62 paraffin-embedded bone metastasis specimens by immunohistochemistry assay. Small interfering RNA (siRNA) was employed to downregulate p62 expression in SPC-A-1 and A549 cells. Cell proliferation and migration ability were tested by CCK8, CCF and Transwell assays respectively. Autophagy was induced by Rapamycin or inhibited by Atg 7 knockout/Chloroquine in A549 cells and p62 and LC3II/I expression were analyzed. After subcutaneous inoculation or intracardial injection of A549 cells into nude mice, the effect of p62 downregulation in vivo was analyzed by histopathological examination. The results showed that p62, LC3B and Beclin 1 mRNA and protein were all overexpressed in bone metastasis tissues (all P<0.01). Patient samples with high p62 expression levels were significantly associated with more bone lesions (>3), shorter overall survival rates and shorter progression free survival rates compared with patients having lower p62 expression (P=0.014, P=0.003, P=0.048, respectively). Cox regression analysis identified p62 expression as an independent prognostic indicator of overall survival of patients with bone metastasis (P=0.007). In vitro p62 downregulation inhibited SPC-A-1 and A549 cells migration but had no effect on cell proliferation. After autophagy induction or inhibition, p62 expression involved in autophagy flux and changed inconsistently according to the switch of LC3I to LC3II in different autophagy conditions. In vivo p62 downregulation had no effect on growth of subcutaneous tumor. Lung or bone metastasis lesion was not found in all mice model. These findings suggested that p62 overexpression promotes tumor cell invasion out of LC3-dependent autophagy, which could be used a potential prognostic biomarker and therapeutic target for bone metastasis of lung adenocarcinoma.

Selective Autophagy Receptor p62/SQSTM1, a Pivotal Player in Stress and Aging

“…Loss of p62 leads to accelerated aging due to a decline in proteostasis, dysregulation of signaling pathways, and inability to sufficiently respond to oxidative stress. However, overexpression of p62 has potential detrimental effects, including accumulation of cellular p62-aggregates ( Kumar et al, 2021 ), tumorigenesis and metastasis induction ( Zatloukal et al, 2007 ; Mathew et al, 2009 ; Li D. et al, 2021 ), and mislocalization of the protein ( Kurosawa et al, 2015 ). In order for p62 overexpression to be beneficial, global coordination of the induction of the 30 + autophagy genes ( Wong et al, 2020b ) by, for example, transcription factors FOXO and TFEB ( Lapierre et al, 2015 ) may enhance autophagy protein levels and increase autophagic flux.…”

“…Further, p62 overexpression promotes bone metastasis by stimulating migration, but not proliferation, of lung adenocarcinoma. High expression of p62 was associated with poor prognosis in patients with bone metastasis ( Li D. et al, 2021 ). p62-induced tumorigenesis reveals an important concern when considering p62 induction as a potential therapeutic via autophagy induction.…”

Fatty Acid Binding Protein 6 Inhibition Decreases Cell Cycle Progression, Migration and Autophagy in Bladder Cancers

“…Meanwhile, LC3B-II was downregulated by FABP6 knockdown. On the other hand, knockdown of p62 inhibits proliferation and migration in lung adenocarcinoma [26]. Accordingly, the autophagic flux, proliferation, and migration might be inhibited by p62 reduction in FABP6 knockdown BC cells.…”

Immunoexpression of p62/SQSTM1/Sequestosome‑1 in human primary and recurrent IDH1/2 wild‑type glioblastoma: A pilot study

“…Among the ATGs, a multifunctional protein considered autophagy adaptor is represented by p62, also named sequestosome 1 (SQSTM 1) (15,16); in particular, this protein may directly interact with microtubule-associated protein light chain 3 (LC3), and further, it may be specifically degraded by autophagy (15). Contrastingly, a defective autophagic phenomenon may produce a p62 upregulation in human tumors (17,18). Some reports have documented an evident p62 expression in pancreatic, hepatocellular, mammary, and oral squamous carcinomas, in which aggressive clinicopathological features and poor prognosis have been referred (16)(17)(18)(19)(20).…”

“…Contrastingly, a defective autophagic phenomenon may produce a p62 upregulation in human tumors (17,18). Some reports have documented an evident p62 expression in pancreatic, hepatocellular, mammary, and oral squamous carcinomas, in which aggressive clinicopathological features and poor prognosis have been referred (16)(17)(18)(19)(20).…”