EGF receptor trafficking: consequences for signaling and cancer.

There are many pathways of endocytosis at the cell surface that apparently operate at the same time. With the advent of new molecular genetic and imaging tools, an understanding of the different ways by which a cell may endocytose cargo is increasing by leaps and bounds. In this review we explore pathways of endocytosis that occur in the absence of clathrin. These are referred to as clathrin-independent endocytosis (CIE). Here we primarily focus on those pathways that function at the small scale in which some have distinct coats (caveolae) and others function in the absence of specific coated intermediates. We follow the trafficking itineraries of the material endocytosed by these pathways and finally discuss the functional roles that these pathways play in cell and tissue physiology. It is likely that these pathways will play key roles in the regulation of plasma membrane area and tension and also control the availability of membrane during cell migration.

https://cshperspectives.cshlp.org/content/6/6/a016758.full.pdf

Clathrin-Independent Pathways of Endocytosis

The LIM kinase family consists of just two members: LIM kinase 1 (LIMK1) and LIM kinase 2 (LIMK2). With uniquely organised signalling domains, LIM kinases are regulated by several upstream signalling pathways, principally acting downstream of Rho GTPases to influence the architecture of the actin cytoskeleton by regulating the activity of the cofilin family proteins cofilin1, cofilin2 and destrin. Although the LIM kinases are very homologous, particularly when comparing kinase domains, there is emerging evidence that each may be subject to different regulatory pathways and may contribute to both distinct and overlapping cellular and developmental functions. Normal central nervous system development is reliant upon the presence of LIMK1, and its deletion has been implicated in the development of the human genetic disorder Williams syndrome. Normal testis development, on the other hand, is disrupted by the deletion of LIMK2. In addition, the possible involvement of each kinase in cardiovascular disorders as well as cancer has recently emerged. The LIM kinases have been proposed to play an important role in tumour-cell invasion and metastasis; fine-tuning the balance between phosphorylated and non-phosphorylated cofilin may be a significant determinant of tumour-cell metastatic potential. In this review, we outline the structure, regulation and function of LIM kinases and their functions at cellular and organismal levels, as well as their possible contributions to human disease.

LIM kinases: function, regulation and association with human disease

The mammalian genome encodes 49 proteins that possess a PX (phox-homology) domain, responsible for membrane attachment to organelles of the secretory and endocytic system via binding of phosphoinositide lipids. The PX domain proteins, most of which are classified as SNXs (sorting nexins), constitute an extremely diverse family of molecules that play varied roles in membrane trafficking, cell signalling, membrane remodelling and organelle motility. In the present review, we present an overview of the family, incorporating recent functional and structural insights, and propose an updated classification of the proteins into distinct subfamilies on the basis of these insights. Almost all PX domain proteins bind PtdIns3P and are recruited to early endosomal membranes. Although other specificities and localizations have been reported for a select few family members, the molecular basis for binding to other lipids is still not clear. The PX domain is also emerging as an important protein-protein interaction domain, binding endocytic and exocytic machinery, transmembrane proteins and many other molecules. A comprehensive survey of the molecular interactions governed by PX proteins highlights the functional diversity of the family as trafficking cargo adaptors and membrane-associated scaffolds regulating cell signalling. Finally, we examine the mounting evidence linking PX proteins to different disorders, in particular focusing on their emerging importance in both pathogen invasion and amyloid production in Alzheimer's disease.

Insights into the PX (phox-homology) domain and SNX (sorting nexin) protein families: structures, functions and roles in disease

The epidermal growth factor receptor (EGFR) is a member of the EGFR family of receptor tyrosine kinases (RTKs). EGFR activation via ligand binding results in signaling through various pathways ultimately resulting in cellular proliferation, survival, angiogenesis, invasion, and metastasis. Aberrant expression or activity of EGFR has been strongly linked to the etiology of several human epithelial cancers including but not limited to head and neck squamous cell carcinoma (HNSCC), non-small cell lung cancer (NSCLC), colorectal cancer (CRC), breast cancer, pancreatic cancer, and brain cancer. Thus intense efforts have been made to inhibit the activity of EGFR by designing antibodies against the ligand binding domains (cetuximab and panitumumab) or small molecules against the tyrosine kinase domain (erlotinib, gefitinib, and lapatinib). Although targeting membrane-bound EGFR has shown benefit, a new and emerging role for EGFR is now being elucidated. In this review we will summarize the current knowledge of the nuclear EGFR signaling network, including how it is trafficked to the nucleus, the functions it serves in the nucleus, and how these functions impact cancer progression, survival, and response to chemotherapeutics.

The nuclear epidermal growth factor receptor signaling network and its role in cancer

The small GTPase RhoA and its downstream effectors, the Rho-associated kinase (Rho-kinase) family, are known to regulate cell morphology, motility, and tumor progression via the regulation of actin cytoskeleton rearrangement. In the present study, we evaluated the role of Rho-kinase in the intracellular endocytic trafficking of ligand-induced phosphorylated epidermal growth factor receptor (pEGFR). We investigated the time course of the internalization fate of EGF-induced pEGFR via the early/late endocytic pathway in human fibrosarcoma cell line HT1080 cells using Y-27632, a selective Rho-kinase inhibitor. We found, using confocal immunofluorescence microscopy and Western blot analysis, a large accumulation of pEGFR in the nuclei of HT1080 cells. In contrast, we observed decreased amounts of the pEGFR-positive staining in the nuclei along with an accumulation of cytosolic pEGFR staining when the cells were incubated for 15–30 min in the presence of Y-27632, implying that an aberrant endocytic trafficking mechanism of pEGFR occurs in HT1080 cells whereby pEGFR might be selectively translocated into the nucleus. Moreover, we demonstrated that after 15-min of stimulation with Texas Red-EGF, increasing numbers of pEGFR-positive staining that had colocalized with Texas Red-EGF-positive punctate staining were seen in the cytoplasm of HT1080 cells but after 30-min of stimulation, most of this staining had disappeared from the cytoplasm and a large accumulation of pEGFR-positive staining appeared in the nucleus. Thus, nuclear accumulation of pEGFR appears to occur in an EGF-dependent manner. In contrast, such nuclear pEGFR-positive staining was not seen in the Y-27632-treated cells. Furthermore, silencing of RhoA or Rho-kinases I/II by sequence specific siRNAs considerably inhibited the EGF-dependent nuclear accumulation of pEGFR. Collectively, these results provide the first evidence that Rho-kinase signaling pathway plays a suppressive role in the intracellular vesicle trafficking of pEGFR via the endocytic pathway and that an increased Rho-kinase activity leads to the attenuation of the normal endocytic vesicular traffic of pEGFR via the early/late endocytic pathway, instead causing pEGFR to be trafficked out of the endocytic vesicles into the nucleus.

A novel role of Rho-kinase in the regulation of ligand-induced phosphorylated EGFR endocytosis via the early/late endocytic pathway in human fibrosarcoma cells

Background: Prevalence of obesity is increasing worldwide, and the Middle East is not an exception to this rise. Bariatric surgery is an effective treatment for obesity in terms of weight loss and remission of metabolic syndrome and has become more popular in recent years. Methods: This is a retrospective cohort study of 69 patients who underwent bariatric surgery at Mediclinic to 1.02 ± 0.26 and 3.50 ± 0.93 to 3.4 ± 0.98 respectively. (P<0.08) AST and ALT improved from 27.85 ± 18.39 to 15.24 ± 4.07 and 40.58 ± 35.49 to 17.84 ± 7.37 respectively at 12 months postoperatively. Only one patient developed postoperative peritonitis causing sepsis. Conclusions: The results show that bariatric surgery was effective in achieving weight loss as well as improvement in lipid and liver profile over a follow up period of one year. Further studies are needed to see whether favorable outcomes of bariatric surgery can be sustained over long term in this mixed population.

/pdf/efficacy-of-bariatric-surgery-in-improving-the-uodtx8yt.pdf

Efficacy of Bariatric Surgery in Improving the Anthropomertics and Metabolic Outcomes: A Retrospective Study from A Single Private Center in Dubai, UAE

Background: Obesity has increased rapidly worldwide in last few decades. According to World Obesity Federation 2018, the prevalence of obesity in UAE amongst Emirati aged 18-69 years has been reported as 32.2% vs 38.5% living with obesity vs overweight in men and 41.8% vs 29.3% living with obesity vs overweight in women. There are many myths amongst general public about obesity. Aim: The objective of the study was to address public questions through online forum regarding weight management. Methods: In this cross-sectional observational study qualitative analysis was done. It was conducted quarterly at Mediclinic City and Parkview Hospital in Dubai from August 2020-September 2021. An online zoom meeting was made available to the public. People who wanted to attend the session registered via dedicated email address. A certified dietician, endocrinologist and bariatric surgeon were available to answer peoples questions. Results: 6 online forums have been conducted. 163 (range 10-90) people attended. Three themes were constructed during data analysis. 1- Diet: what is the best diet and about caloric intake. 2- Insulin resistance or hormone imbalance is responsible for weight gain. 3- Misinformation and unrealistic expectations about bariatric surgery. Feedback from audience was: it was interactive, fun and informative session, it is good to know that it is not my fault and I need to get help. Conclusion: Our results show that patients need support throughout their weight management journey. Healthcare professionals need to be more aware of patients perceptions about weight management so that they can be addressed in consultations. We need more online support sessions facilitated by healthcare professionals. Key words: obesity, zoom meeting, weight management

Biborka Bereczky

Papers

A novel role of Rho-kinase in the regulation of ligand-induced phosphorylated EGFR endocytosis via the early/late endocytic pathway in human fibrosarcoma cells

Efficacy of Bariatric Surgery in Improving the Anthropomertics and Metabolic Outcomes: A Retrospective Study from A Single Private Center in Dubai, UAE

Bridging the gap: A qualitative analysis of online public forum with healthcare professionals in bursting myths about weight management.