Complex Rab4-Mediated Regulation of Endosomal Size and EGFR Activation
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Published OnlineFirst February 4, 2020; DOI: 10.1158/1541-7786.MCR-19-0052 MOLECULAR CANCER RESEARCH | SIGNAL TRANSDUCTION AND FUNCTIONAL IMAGING Complex Rab4-Mediated Regulation of Endosomal Size and EGFR Activation Kate Tubbesing1, Jamie Ward1, Raymond Abini-Agbomson1, Aditi Malhotra1, Alena Rudkouskaya1, Janine Warren1, John Lamar1, Nina Martino1, Alejandro P. Adam1,2, and Margarida Barroso1 ABSTRACT ◥ Early sorting endosomes are responsible for the trafficking and exhibited prolonged and increased EGF-induced activation of function of transferrin receptor (TfR) and EGFR. These receptors EGFR upon phosphorylation at tyrosine-1068 (EGFR-p1068). play important roles in iron uptake and signaling and are critical for Rab4A overexpression in MCF10A cells produced EEA1-positive breast cancer development. However, the role of morphology, enlarged endosomes that displayed prolonged and amplified receptor composition, and signaling of early endosomes in breast EGF-induced EGFR-p1068 activation. Knockdown of Rab4A cancer remains poorly understood. A novel population of enlarged lead to increased endosomal size in MCF10A, but not in early endosomes was identified in breast cancer cells and tumor MDA-MB-231 cells. Nevertheless, Rab4A knockdown resulted xenografts but not in noncancerous MCF10A cells. Quantitative in enhanced EGF-induced activation of EGFR-p1068 in MDA- analysis of endosomal morphology, cargo sorting, EGFR activa- MB-231 as well as downstream signaling in MCF10A cells. tion, and Rab GTPase regulation was performed using super- Altogether, this extensive characterization of early endosomes resolution and confocal microscopy followed by 3D rendering. in breast cancer cells has identified a Rab4-modulated enlarged MDA-MB-231 breast cancer cells have fewer, but larger EEA1- early endosomal compartment as the site of prolonged and positive early endosomes compared with MCF10A cells. Live-cell increased EGFR activation. imaging indicated dysregulated cargo sorting, because EGF and Tf traffic together via enlarged endosomes in MDA-MB-231, but Implications: Enlarged early endosomes play a Rab4-modulated not in MCF10A. Large EEA1-positive MDA-MB-231 endosomes role in regulation of EGFR activation in breast cancer cells. Introduction pathways are initiated from this dynamic organelle (8, 9). Thus, while multiple receptors share an initial endocytosis pathway, their cellular Characterization of the morphology and subcellular localization of fate can differ substantially. For example, Tf bound to its receptor early endosomes (EE) is essential for the understanding of receptor delivers iron into cells via the early and recycling endocytic path- trafficking and signaling in cancer cells. Recently, the endocytic way (10), whereas LDL, which plays a key role in lipid metabolism, is pathway has been shown to be defective in various human can- released from LDLR in EE and delivered to late endosomes/lyso- cers (1, 2). Furthermore, clathrin-dependent and -independent endo- somes (11). Moreover, EGF-induced internalization of EGFR into EEs cytosis show significant alterations in several cancer cell lines (3–5). is required for its signaling function, and EGFR's kinase activity is Importantly, the size and cellular distribution of endosomes have been downregulated via the ubiquitination-dependent late endosomal/lyso- suggested as a potential biomarker in cancer (6). Moreover, peri- somal pathway (12). Therefore, studying the altered endocytic traf- nuclear endosomal signaling complexes have been shown to play a ficking of Tf-TfR, EGF-EGFR, and LDL-LDLR in cancer is crucial to crucial role in the regulation of signaling cascades involved in cancer advance our understanding of the crosstalk between cell signaling and progression (7). However, many aspects of EE function, regulation, metabolism. and morphology in breast cancer cells remain unclear. Endosomal compartments are identified and regulated by one or Membrane-bound receptors involved in nutrient uptake, for exam- more small Rab-GTPases, which modulate essential membrane func- ple, transferrin-receptor (TfR) and low-density lipoprotein (LDL), as tions via interactions with Rab effector proteins (9, 13). Rab5 is an well as in cell signaling, for example, EGFR, play an important role in important regulator of the EEs (9). Two well-characterized Rab5 cancer development and progression. These receptors are endocytosed effectors, EEA1 (EE Antigen 1) and APPL1, can occupy the same or via multiple internalization pathways into EE, which act as a literal separate EEs (14, 15). Altered expression and activity levels of Rab “fork in the road,” as both the endocytic recycling and lysosomal GTPases affect the endocytosis, degradation, and recycling of mem- brane-bound receptors, leading to increased cancer cell proliferation 1 and motility as well as metastatic behavior (1, 2, 16, 17). Department of Molecular and Cellular Physiology, Albany Medical College, fi Albany, New York. 2Department of Ophthalmology, Albany Medical College, Rab4 is the most commonly ampli ed Rab GTPase in invasive Albany, New York. breast carcinoma (4). Rab4 and Rab11 work in a coordinated manner to regulate the fast and slow recycling compartments, respectively Note: Supplementary data for this article are available at Molecular Cancer – fl Research Online (http://mcr.aacrjournals.org/). (18 20). Moreover, Rab4 was shown to in uence Tf-mediated cellular iron accumulation (21). Rab4 inactivation, through expres- Corresponding Author: Margarida Barroso, Albany Medical College, 47 New Scotland Av, Albany, NY 12208. Phone: 518-262-6435; Fax: 518-262-8101; E-mail: sion of either a dominant-negative Rab4-S22N mutation or a Rab4 [email protected] GTPase activating protein (TBC1D16), increases EGFR degrada- tion (22, 23) and weakens the invasive behavior of breast cancer Mol Cancer Res 2020;18:757–73 cells in vivo (4). As the regulation of EGFR trafficking and signaling doi: 10.1158/1541-7786.MCR-19-0052 involves multiple Rab proteins, the role of Rab4 in EGFR regulation Ó2020 American Association for Cancer Research. remains unclear (24). AACRJournals.org | 757 Downloaded from mcr.aacrjournals.org on October 1, 2021. © 2020 American Association for Cancer Research. Published OnlineFirst February 4, 2020; DOI: 10.1158/1541-7786.MCR-19-0052 Tubbesing et al. EEs have been characterized as tubulovesicular compartments with Tumor xenografts an average diameter between 100 and 500 nm (9, 25). In this study, All animal procedures were conducted with the approval of the super-resolution (SR) microscopy, time-lapse live-cell imaging, and Institutional Animal Care and Use Committee at Albany Medical 3D whole-cell quantitative microscopy approaches, as well as immu- College, which is American Association for Laboratory Animal Care nostaining and immunoblotting signaling assays were used to char- accredited. Human tumor xenografts were generated as described in acterize an enlarged endosomal population that is also the site of ref. 27. increased and prolonged EGF-induced EGFR activation upon phos- phorylation at tyrosine 1068 (EGFR-p1068), in aggressive triple- 3D dSTORM microscopy negative MDA-MB-231 cells but not in nontransformed mammary Cells were preincubated for 30 minutes with CI medium and epithelial MCF10A cells. Furthermore, Rab4A overexpression led to an incubated with 20 mg/mL AF647-Tf in CI medium for 1 hour, prior increase in EEA1-positive endosomal size as well as an extended and to PBS washes and fixation with 4% PFA. 3D dSTORM microscopy elevated EGF-induced EGFR-p1068 activation in those enlarged and postprocessing image analysis was performed as described in endosomes in MCF10A cells. Unexpectedly, Rab4A knockdown led ref. 28 and in Supplementary Methods. to an increased endosomal size in MCF10A, but not in MDA-MB-231 cells. Nevertheless, Rab4A-depleted MDA-MB-231 cells displayed an Confocal and Airyscan microscopy fi elevated EGF-induced activation of EGFR-p1068. These ndings Zeiss LSM880 with Fast Airyscan detector or LSM510 (Zeiss) were establish enlarged EEs in breast cancer cells as central players in the used to collect z-stack images. Fast Airyscan was performed at Nyquist fi regulation of cargo traf cking and cell signaling, Here, we suggest a sampling and using SR settings. For whole-cell analysis, z-stack images complex role for Rab4 in the regulation of endosomal size as well as of were collected to visualize cells from top to bottom, and for live-cell intensity and duration of EGFR activation. imaging, 3–5 images per z-stack were collected per time point. Air- yscan processing (pixel reassignment) was performed in Zen Black Materials and Methods software under default settings. Live-cell imaging is described in Supplementary Methods. Cell culture Cells were purchased from ATCC and tested routinely for Myco- Colocalization analysis plasma. MCF10A cells were cultured in DMEM/F12 with 5% horse Pearson correlation coefficient in z-stacks was determined using serum, 20 ng/mL EGF, 0.5 mg/mL hydrocortisone, 100 ng/mL cholera “coloc” module from Imaris software (Bitplane, Inc.). For statistical toxin, 10 mg/mL bovine insulin, and penicillin/streptomycin. Human analysis, at least 3 z-stack whole images per condition were analyzed. breast cancer cells were cultured in DMEM with 10% FBS, 4 mmol/L Extended description of the colocalization analysis is found in Sup- L-glutamine, and 10 mmol/L HEPES, pH 7.4. Cells were passaged less plementary Methods and Supplementary Fig. S1. than 15 times. No further cell line authentication was