The prognostic value of p62 in solid tumor patients: a meta-analysis

Spitz Spindle Cell/Reed Nevus With SQSTM1 :: NTRK2 Fusion and Atypical Features in an Older Male Patient: A Case Report and Review of Literature

Spitz lesions display a set of genetic alterations that differ from classical melanocytic lesions: examples include mutations in HRAS and fusions involving ALK, ROS1, MET, MAP3K8, BRAF, and the NTRK genes. We present a Spitz spindle cell/Reed nevus with atypical junctional features and an NTRK2 translocation in a patient of unusual age. The patient was a 61-year-old man with a pigmented brown flat 6 mm lesion growing on the skin over the left scapula. The lesion was composed of spindled and epithelioid melanocytes and was arranged in nests with some scattered focal pagetoid cells as well as intraepidermal nests at the center of the lesion and occasional mitotic figures. The melanocytes showed diffuse staining for pan-Trk antibodies. p16 staining was focally and weakly positive. The cells showed staining for HMB-45, MART-1, and tyrosinase, whereas they were negative for PRAME, ALK-1, and ROS-1 immunostaining. BAP-1 was preserved. Next-generation sequencing detected a SQSTM1::NTRK2 fusion and showed no alterations of ALK, ROS1, RET, NTRK1, and NTRK3 genes, as well as no pathogenic variants of BRAF. Fluorescent in situ hybridization showed NTRK2 translocation in all melanocytes evaluated. This case presents a Spitz nevus with a rare translocation in an older patient.

Metabolic stress induces a double-positive feedback loop between AMPK and SQSTM1/p62 conferring dual activation of AMPK and NFE2L2/NRF2 to synergize antioxidant defense

Co-occurring mutations in KEAP1 in STK11/LKB1-mutant NSCLC activate NFE2L2/NRF2 to compensate for the loss of STK11-AMPK activity during metabolic adaptation. Characterizing the regulatory crosstalk between the STK11-AMPK and KEAP1-NFE2L2 pathways during metabolic stress is crucial for understanding the implications of co-occurring mutations. Here, we found that metabolic stress increased the expression and phosphorylation of SQSTM1/p62, which is essential for the activation of NFE2L2 and AMPK, synergizing antioxidant defense and tumor growth. The SQSTM1-driven dual activation of NFE2L2 and AMPK was achieved by inducing macroautophagic/autophagic degradation of KEAP1 and facilitating the AXIN-STK11-AMPK complex formation on the lysosomal membrane, respectively. In contrast, the STK11-AMPK activity was also required for metabolic stress-induced expression and phosphorylation of SQSTM1, suggesting a double-positive feedback loop between AMPK and SQSTM1. Mechanistically, SQSTM1 expression was increased by the PPP2/PP2A-dependent dephosphorylation of TFEB and TFE3, which was induced by the lysosomal deacidification caused by low glucose metabolism and AMPK-dependent proton reduction. Furthermore, SQSTM1 phosphorylation was increased by MAP3K7/TAK1, which was activated by ROS and pH-dependent secretion of lysosomal Ca2+. Importantly, phosphorylation of SQSTM1 at S24 and S226 was critical for the activation of AMPK and NFE2L2. Notably, the effects caused by metabolic stress were abrogated by the protons provided by lactic acid. Collectively, our data reveal a novel double-positive feedback loop between AMPK and SQSTM1 leading to the dual activation of AMPK and NFE2L2, potentially explaining why co-occurring mutations in STK11 and KEAP1 happen and providing promising therapeutic strategies for lung cancer.Abbreviations: AMPK: AMP-activated protein kinase; BAF1: bafilomycin A1; ConA: concanamycin A; DOX: doxycycline; IP: immunoprecipitation; KEAP1: kelch like ECH associated protein 1; LN: low nutrient; MAP3K7/TAK1: mitogen-activated protein kinase kinase kinase 7; MCOLN1/TRPML1: mucolipin TRP cation channel 1; MEFs: mouse embryonic fibroblasts; MTORC1: mechanistic target of rapamycin kinase complex 1; NAC: N-acetylcysteine; NFE2L2/NRF2: NFE2 like bZIP transcription factor 2; NSCLC: non-small cell lung cancer; PRKAA/AMPKα: protein kinase AMP-activated catalytic subunit alpha; PPP2/PP2A: protein phosphatase 2; ROS: reactive oxygen species; PPP3/calcineurin: protein phosphatase 3; RPS6KB1/p70S6K: ribosomal protein S6 kinase B1; SQSTM1/p62: sequestosome 1; STK11/LKB1: serine/threonine kinase 11; TCL: total cell lysate; TFEB: transcription factor EB; TFE3: transcription factor binding to IGHM enhancer 3; V-ATPase: vacuolar-type H+-translocating ATPase.

Immunohistochemistry analysis of autophagy-related proteins Beclin-1, p62/SQSTM1, and LC3B in breast carcinoma progression to bone metastasis

Autophagy is a catabolic pathway involved both in tissue homeostasis and in cellular response to stress. The precise role of autophagy in cancer is still undefined and seems to depend on the tumor stage, appearing tumor-suppressive in physiological conditions and helpful to tumor progression in the established tumor. Here we analyzed by immunohistochemistry Beclin-1, p62, and LC3B, autophagic markers, in human specimens of normal breast, bone metastasis together with pair-matched invasive breast carcinoma of no special type (IBC-NST) as well as non-metastatic breast carcinoma, to disclose the possibility that they could be early prognostic indicators of the evolution of the disease toward the worst outcome. Different regions of metastatic carcinomas, i.e., areas adjacent to the tumor without signs of neoplastic growth, dysplastic lesions, and areas with invasive growth were considered. The pattern of autophagic parameters showed differences among the stages of breast carcinoma progression with a trend that indicated the activation of autophagic process in normal breast (Beclin-1 more elevated than p62), a pattern that was maintained in non-metastatic carcinoma. As the neoplasia proceeds with malignancy, the modification of the pattern of expression of autophagic markers (low ratio between Beclin-1 and p62) in areas of invasive growth of carcinomas suggested inhibition of the process. Of note, the parameters showed a different pattern in bone metastasis with respect to bone metastatic (bm)-IBC-NST, suggesting the reactivation of the autophagic process in the new growth site, helpful to the colonization. The course of autophagy markers during tumor progression could have a prognostic value towards bone metastasis and reveal different roles of the process in different phases of neoplastic growth. The understanding of the role of autophagy in bone metastasis could disclose new therapeutic targets to improve the conditions of patients.

Beyond self‑eating: Emerging autophagy‑independent functions for the autophagy molecules in cancer (Review)

Autophagy is a conserved catabolic process that controls organelle quality, removes misfolded or abnormally aggregated proteins and is part of the defense mechanisms against intracellular pathogens. Autophagy contributes to the suppression of tumor initiation by promoting genome stability, cellular integrity, redox balance and proteostasis. On the other hand, once a tumor is established, autophagy can support cancer cell survival and promote epithelial‑to‑mesenchymal transition. A growing number of molecules involved in autophagy have been identified. In addition to their key canonical activity, several of these molecules, such as ATG5, ATG12 and Beclin‑1, also exert autophagy‑independent functions in a variety of biological processes. The present review aimed to summarize autophagy‑independent functions of molecules of the autophagy machinery and how the activity of these molecules can influence signaling pathways that are deregulated in cancer progression.

Cross-talk between mutant p53 and p62/SQSTM1 augments cancer cell migration by promoting the degradation of cell adhesion proteins

Missense mutations in the TP53 gene, encoding the p53 tumor suppressor, are very frequent in human cancer. Some of those mutations, particularly the more common (“hotspot”) ones, not only abrogate p53’s tumor suppressor activities but also endow the mutant protein with oncogenic gain of function (GOF). We report that p53^R273H, the most common p53 mutant in pancreatic cancer, interacts with the SQSTM1/p62 protein to accelerate the degradation of cell adhesion proteins. This enables pancreatic cancer cells to detach from the epithelial sheet and engage in individualized cell migration, probably augmenting metastatic spread. By providing insights into mechanisms that underpin mutant p53 GOF, this study may suggest ways to interfere with the progression of cancers bearing particular p53 mutants.

Missense mutations in the p53 tumor suppressor abound in human cancer. Common (“hotspot”) mutations endow mutant p53 (mutp53) proteins with oncogenic gain of function (GOF), including enhanced cell migration and invasiveness, favoring cancer progression. GOF is usually attributed to transcriptional effects of mutp53. To elucidate transcription-independent effects of mutp53, we characterized the protein interactome of the p53^R273H mutant in cells derived from pancreatic ductal adenocarcinoma (PDAC), where p53^R273H is the most frequent p53 mutant. We now report that p53^R273H, but not the p53^R175H hotspot mutant, interacts with SQSTM1/p62 and promotes cancer cell migration and invasion in a p62-dependent manner. Mechanistically, the p53^R273H-p62 axis drives the proteasomal degradation of several cell junction–associated proteins, including the gap junction protein Connexin 43, facilitating scattered cell migration. Concordantly, down-regulation of Connexin 43 augments PDAC cell migration, while its forced overexpression blunts the promigratory effect of the p53^R273H-p62 axis. These findings define a mechanism of mutp53 GOF.

Association between p62 expression and clinicopathological characteristics in oral leukoplakia

Objective

Oral leukoplakia is keratinized lesions in the buccal mucosa, tongue, and gingiva. It is the most common oral precancerous lesion; oxidative stresses and irrelevant autophagy have been reported to be the cause of oncogenesis. p62, a cytoplasmic protein induced by oxidative stress, is an adaptor protein involved in the formation of protein aggregates and induction and inhibition of autophagy. The inhibition of autophagy induces p62 overexpression and promotes oncogenesis via the oncogenic signaling pathway. The aim of the present study was to elucidate the involvement of intracellular expression of p62 in oral leukoplakia and to address its potential clinical implementation as a biomarker to predict malignant transformation.

Material and Methods

Fifty samples from subjects with confirmed oral leukoplakia were evaluated by immunohistochemical staining for the expression of p62, 8-hydroxy-2'-deoxyguanosine (8-OHdG), Ki67, and p53. Univariate and multivariate logistic regression analyses were performed to evaluate the association between p62, 8-OHdG, Ki67, and p53 and clinical characteristics, including epithelial dysplasia.

Results

Significant associations were observed between p62 expression in the nucleus, p62 aggregation, and epithelial dysplasia (adjusted odds ratio [OR] = 5.75; 95% confidence interval [CI]: [1.28, 26.2]; .024 and OR = 6.16; 95% CI: [1.01, 37.4]; .048, respectively). The expression of p62 in the cytoplasm and the levels of 8-OHdG, Ki67, and p53 were not significantly associated with epithelial dysplasia. A significant relationship was found between p62 expression in the nucleus and p53 expression (OR = 3.94; 95% CI: [1.14, 13.6]; .031).

Conclusions

The results suggested that p62 expression in the nucleus and p62 aggregation can be potential markers to predict the malignant transformation of oral leukoplakia.

Hypoxia as a signal for prison breakout in cancer

PURPOSE OF REVIEW

We discuss recent discoveries in hypoxic cellular pathophysiology and explore the interplay between hypoxic malignant cells and other stromal elements. This review will provide an update on the effects of hypoxia on cancer outcomes and therapeutic resistance.

RECENT FINDINGS

Hypoxia has been discovered to be a key driver for tumor progression, both because of impacts on tumor cells and separately on the wider tumor microenvironment. The latter effects occur via epithelial mesenchymal transition, autophagy and metabolic switching. Through epithelial mesenchymal transition, hypoxia both drives metastasis and renders key target tissues receptive to metastasis. Autophagy is a double-edged sword which requires greater understanding to ascertain when it is a threat. Metabolic switching allows tumor cells to access hypoxic survival mechanisms even under normoxic conditions.Every element of the malignant stroma contributes to hypoxia-driven progression. Exosomal transfer of molecules from hypoxic tumor cells to target stromal cell types and the importance of microRNAs in intercellular communication have emerged as key themes.Antiangiogenic resistance can be caused by hypoxia-driven vasculogenic mimicry. Beyond this, hypoxia contributes to resistance to virtually all oncological treatment modalities.

SUMMARY

Recent advances have moved us closer to being able to exploit hypoxic mechanisms to overcome hypoxia-driven progression and therapy failure.

Intranuclear inclusions in hepatocellular carcinoma contain autophagy-associated proteins and correlate with prolonged survival

For decades, intranuclear inclusions in many normal and neoplastic cells have been considered to be mere invaginations of cytoplasm into the nucleus without any notable function or influence on disease. We investigated such inclusions in 75 specimens of hepatocellular carcinoma (HCC). In this context we demonstrate that these inclusions are true inclusions, completely closed and delimited by the nuclear membrane, containing degenerate cell organelles and lysosomal proteins. Moreover, their occurrence was positively associated with patient survival but not with tumour grade or stage. In a standardised area a mean of 124 inclusions per specimen was present in the tumorous liver tissue in contrast to 5 inclusions in the non‐tumorous adjacent section and 89% of all scrutinised HCC showed at least one membrane‐bound nuclear inclusion. Ultrastructural characterisation by transmission electron microscopy revealed degenerative materials such as residues of lysosomes, endoplasmic reticulum and Golgi apparatus within the inclusions. Due to the fact that the content of the inclusions appears to be more condensed than cytoplasm and contains fewer intact cell organelles, we assume that they are not mere invaginations of cytoplasm. Three dimensional (3D) reconstruction of isolated and immunofluorescence stained nuclei showed that the inclusions are completely located within the nucleus without any connection to the cytoplasm. The limiting membrane of the inclusions contained lamin B suggesting nuclear membrane origin. The content of the inclusions stained for the autophagy‐associated proteins p62, ubiquitin, LC3B, cathepsin B and cathepsin D. Triple immunofluorescence staining followed by 3D reconstruction revealed co‐localisation of p62, ubiquitin and LC3B in the same inclusion. Our observations uncover that these inclusions are real inclusions completely surrounded by the nucleus. We propose that the presence of autophagy‐associated proteins and proteases within the inclusions contribute to beneficial survival.

Map1lc3b and Sqstm1 Modulated Autophagy for Tumorigenesis and Prognosis in Certain Subsites of Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) is one of the most common cancer types worldwide and can be divided into three major subsites: buccal mucosal SCC (BMSCC), tongue SCC (TSCC), and lip SCC (LSCC). The autophagy marker microtubule-associated protein light chain 3B (MAP1LC3B) and adaptor sequestosome 1(SQSTM1) are widely used proteins to evaluate autophagy in tumor tissues. However, the role of MAP1LC3B and SQSTM1 in OSCC is not fully understood, particularly in certain subsites. With a tissue microarray comprised of 498 OSCC patients, including 181 BMSCC, 244 TSCC, and 73 LSCC patients, we found that the expression levels of MAP1LC3B and cytoplasmic SQSTM1 were elevated in the tumor tissues of three subsites compared with those in adjacent normal tissues. MAP1LC3B was associated with a poor prognosis only in TSCC. SQSTM1 was associated with poor differentiation in three subsites, while the association with lymph node invasion was only observed in BMSCC. Interestingly, MAP1LC3B was positively correlated with SQSTM1 in the tumor tissues of BMSCC, whereas it showed no correlation with SQSTM1 in adjacent normal tissue. The coexpression of higher MAP1LC3B and SQSTM1 demonstrated a significantly worse disease-specific survival (DSS) and disease-free survival (DFS) in patients with BMSCC and LSCC, but not TSCC. The knockdown of MAP1LC3B and SQSTM1 reduced autophagy, cell proliferation, invasion and tumorspheres of BMSCC cells. Additionally, silencing both MAP1LC3B and SQSTM1 enhanced the cytotoxic effects of paclitaxel in the tumorspheres of BMSCC cells. Taken together, MAP1LC3B and SQSTM1 might modulate autophagy to facilitate tumorigenesis and chemoresistance in OSCC, particularly in BMSCC.

p62/SQSTM1 - steering the cell through health and disease

SQSTM1 (also known as p62) is a multifunctional stress-inducible scaffold protein involved in diverse cellular processes. Its functions are tightly regulated through an extensive pattern of post-translational modifications, and include the isolation of cargos degraded by autophagy, induction of the antioxidant response by the Keap1-Nrf2 system, as well as the regulation of endosomal trafficking, apoptosis and inflammation. Accordingly, malfunction of SQSTM1 is associated with a wide range of diseases, including bone and muscle disorders, neurodegenerative and metabolic diseases, and multiple forms of cancer. In this Review, we summarize current knowledge regarding regulation, post-translational modifications and functions of SQSTM1, as well as how they are dysregulated in various pathogenic contexts.

Cytoplasmic SQSTM1/ P62 Accumulation Predicates a Poor Prognosis in Patients with Malignant Tumor

Aims: SQSTM1/p62, as an autophagy marker, is a key molecule involved in the autophagy process. Recent studies have demonstrated that p62 has a close relationship with tumorigenesis and progression, but the impact of p62 on patients' survival has not been comprehensively understood. Therefore, we conducted this study to assess the expression level of p62 in tumor cells and the prognostic role of p62 expression in various malignant tumors. Methods: We searched PubMed, PubMed Central (PMC), Embase, Ovid and Web of Science databases and identified 30 eligible studies containing 14,072 patients to include in the meta-analysis. The p62 mRNA and protein expression profiles in various tumor tissues and normal tissues were presented according to the Human Protein Atlas (HPA) and the Gene Expression Profiling Interactive Analysis (GEPIA). We also tested the association between p62 mRNA level and patients' survival based on the Cancer Genome Atlas (TCGA) and the Human Protein Atlas (HPA) databases. Results: The expression levels of p62 mRNA and protein varied in different tissues. The p62 proteins were elevated and mainly located in the cytoplasm in some types of tumor compared with the normal tissues. The pooled results indicated that p62 overexpression in tumor tissues was associated with a worse prognosis. In the subgroup analysis, a significant relationship was observed between cytoplasmic p62 accumulation and both overall survival (HR 1.53, 95% CI: 1.03-2.27, P < 0.05) and disease-specific survival (HR 1.60, 95% CI: 1.15-2.24, P < 0.01). The relationship between p62 and worse survival was more evident in early stage tumors. P62 mRNA expression had no significant effect on the patient's survival except of liver cancer. Conclusions: The findings of this meta-analysis highlight the role of p62 as a useful prognostic biomarker for some types of tumor according to different clinicopathologic features, which may contribute to the selection of effective treatment methods for different malignant tumors.

[Lung cancer under stress]

BACKGROUND

Autophagy is a cellular mechanism involved in maintaining cellular homeostasis and warranting cellular survival under stress, and may be therapeutically exploited. Autophagy assessment in vitro is well established, but analysis in formalin-fixed and paraffin-embedded (FFPE) tissue is still poorly standardized. Expression analysis of autophagy-associated markers in diagnostic FFPE tissue aids in translating in vitro findings to the clinic and may contribute to a future quest for predictive markers.

MATERIAL AND METHODS

We have established a reliable visualization of autophagy-related proteins in FFPE tissue by immunohistochemistry, using lung cancer cell lines with functionally modified autophagy states and marker-depletion, respectively, and evaluated the prognostic impact of autophagy-related markers in lung cancer patients.

RESULTS

Dot-like staining was observed for LC3 and p62, representing the degrading autophagic vesicles. Stainings correlated significantly with quantitative protein expression assessed by western blot in cell lines and FFPE tumor tissue. In stage I/II non-small cell lung cancer cases and a large cohort of pulmonary squamous cell carcinomas, dot-like LC3 and p62 staining lacked clear prognostic value, but p62 expression was an independent prognostic factor for shorter survival in both cohorts and using internal validation models.

CONCLUSIONS

Valid visualization of autophagy-related markers in FFPE tissue is feasible. We could not demonstrate a clear prognostic role of autophagy status as deducted from LC3-p62 co-expression. The autophagy independent role of p62 in lung cancer warrants further investigation, as well as crosstalk with other stress factors or the role of autophagy induction during or after treatment.

The macroenviromental control of cancer metabolism by p62

Metabolic reprogramming is a hallmark of cancer, but most studies focus on the molecular alterations in cancer cells and much less is known on the role of cancer metabolism, from a holistic perspective, for tumor initiation and progression. Increasing epidemiological evidence highlights the tremendous impact that cancer progression has on the host metabolism, especially in cachexia. However, how this benefits the tumor still is not completely understood. Here we review current studies on fatty acid oxidation in tumor cells as a potential therapeutic target in cancer, and how the redistribution of lipids from fat reservoirs to the cancer cell in the micro- and macro-environment impacts tumorigenesis by helping the tumor fulfill its energetic demands at the expense of fat. In this context, we also discuss the critical role of the signaling adaptor p62/Sequestosome 1(SQSTM1) in adipocytes in mediating tumor-induced fat reprograming and the feedback of adipose tissue on tumor aggressiveness via osteopontin and its potential implications in obesity-promoted cancer and fat cachexia. Collectively these studies highlight the importance of the symbiotic collaboration between adipose tissue and tumor to modulate the cancer metabolic fitness.

Expression Analysis of Autophagy Related Markers LC3B, p62 and HMGB1 Indicate an Autophagy-Independent Negative Prognostic Impact of High p62 Expression in Pulmonary Squamous Cell Carcinomas

Autophagy is involved in maintaining cellular homeostasis under stress conditions. It also plays an important role in various diseases including cancer. Pulmonary squamous cell carcinomas (pSQCC) at present lack targetable molecular alterations, and demand alternative therapeutic options. We assessed the expression levels of autophagy related proteins LC3B, p62, and HMGB1 in 271 primary resected pSQCC by immunohistochemistry, in correlation with clinical and pathological parameters, as a rationale for a potential autophagy directed therapy. LC3B, p62, and HMGB1 staining showed various patterns. LC3B^highp62^low levels, suggested to indicate intact activated autophagy, were associated with prolonged disease specific survival (DSS) and LC3B^highp62^high levels, indicating activated but late stage impaired autophagy, with shorter DSS (p = 0.024). p62^high expression regardless of LC3B, however, showed an even stronger association with shorter DSS (p = 0.015) and was also an independent negative prognostic factor in multivariate analysis (HR = 2.99; 95% CI 1.38–6.52; p = 0.006). HMGB1 expression correlated neither with the expression of LC3B and p62, nor with patients’ outcome. Different states of autophagy characterized by distinct p62 and LC3B expression patterns may be linked to patient’s prognosis in pSQCC. Our results, however, point also to an autophagy independent role of p62 with an even more pronounced prognostic impact compared to autophagy related p62.