Recycling machinery of integrin coupled with focal adhesion turnover via RAB11-UNC13D-FAK axis for migration of pancreatic cancer cells

Abstract

Background: Recycling of integrin via endosomal vesicles is critical for the migration of cancer cells, which leads to the metastasis of pancreatic cancer and devastating cancer-related death. So, new diagnostic and therapeutic molecules which target the recycling of endosomal vesicles need to be developed.

Methods: Public databases including TCGA, ICGC, GSE21501, GSE28735, and GENT are analyzed to derive diagnostic and therapeutic targets. To reveal biological roles and underlying mechanisms of molecular targets, various molecular biological experiments were conducted.

Results: First, we identified UNC13D's overexpression in patients with pancreatic cancer (n = 824) and its prognostic significance and high hazard ratio (HR) in four independent pancreatic cancer cohorts (TCGA, n = 178, p = 0.014, HR = 3.629; ICGC, n = 91, p = 0.000, HR = 4.362; GSE21501, n = 102, p = 0.002, HR = 2.339; GSE28735, n = 45, p = 0.022, HR = 2.681). Additionally, its expression is associated with the clinicopathological progression of pancreatic cancer. Further biological studies have shown that UNC13D regulates the migration of pancreatic cancer cells by coupling the exocytosis of recycling endosomes with focal adhesion turnover via the regulation of FAK phosphorylation. Immunoprecipitation and immunocytochemistry showed the formation of the RAB11-UNC13D-FAK axis in endosomes during integrin recycling. We observed that UNC13D directly interacted with the FERM domain of FAK and regulated FAK phosphorylation in a calcium-dependent manner. Finally, we found co-expression of UNC13D and FAK showed the poorest survival (TCGA, p = 0.000; ICGC, p = 0.036; GSE28735, p = 0.006).

Conclusions: We highlight that UNC13D, a novel prognostic factor, promotes pancreatic cancer progression by coupling integrin recycling with focal adhesion turnover via the RAB11-UNC13D-FAK axis for the migration of pancreatic cancer cells.

Keywords: FAK; Focal adhesion; Integrin; Migration; Pancreatic cancer; Prognosis; RAB11; UNC13D.

Fig. 1

Expression level and prognostic significance of UNC13D and FAK (PTK2) in pancreatic cancer. A Comparison between cancer and matched normal pancreas tissue from GSE28735 cohort (n = 45, Wilcoxon signed rank test). B Comparison between cancer and normal pancreas tissues from TCGA and GTEx cohort (n = 350, Mann–Whitney U test). C Comparison between cancer and normal pancreas tissues from GEO cohorts in GENT database (n = 429, Mann–Whitney U test). D Expression level of UNC13D in patients of each subgroup of pancreatic cancer (TCGA, n = 178). E Kaplan–Meier survival analysis of HCC patients according to the UNC13D and FAK (PTK2) gene expression. Overall survival in TCGA (n = 178), ICGC (n = 91), GSE21501(n = 102), and GSE28735 (n = 45) were examined according to the UNC13D, FAK (PTK2), or both expression (Log-rank test). The p value is provided inside each graph

Fig. 2

UNC13D regulates the migration of pancreatic cancer cells via focal adhesion (FA) turnover. A, B Boyden chamber and wound healing assay of cell migration capacity upon UNC13D knockdown in ASPC-1 and PANC-1. Data are presented as the mean ± SD. Two-tailed unpaired Student T test: **p < 0.01 and ***p < 0.001. The quantification data shown are representative of three independent experiments. C Analysis of cell invasion capacity upon UNC13D knockdown in MIA PaCa-2 and PANC-1 cells. The quantification data are presented as the mean ± SD of three independent experiments. Two-tailed unpaired Student T test: **p < 0.01. D Gene set enrichment assay (GSEA) of differentially expressed genes (DEGs) between UNC13D-high vs -low groups in the TCGA cohort indicates the enrichment of the integrin pathway and FA pathway. E FA disassembly assay using nocodazole (NDZ) shows UNC13D regulates FA turnover of pancreatic cancer cells. UNC13D knockdown slows FA disassembly. CAPAN-1 shSCR or shUNC13D were starved, left untreated or incubated with 10 μM nocodazole. After 4 h, nocodazole was washed out at different times to allow microtubule regrowth to trigger FA disassembly. The cells were then fixed and immunostained with anti-PXN antibody. Quantification of FAs number was obtained from an average of ten cells of each condition from three independent experiments. Data were shown as mean ± SD of three independent experiments. Two-tailed unpaired Student T test: *p < 0.05. Scale bar, 10 μm. F FAK autophosphorylation and its total form were evaluated by western blot at different times of nocodazole washed-out as in E. FAK autophosphorylation was quantified and normalized to total FAK expression

Fig. 3

RAB11-UNC13D-FAK axis in recycling endosomes regulates the phosphorylation of FAK. A UNC13D knockdown in CAPAN-1 and PANC-1 cells decreased FAK/PXN signaling, which was measured by p-FAK, p-PXN, FAK, and PXN. Data are presented as the mean ± SD. The experiments were independently performed at least three times. Statistical analysis was performed using Student’s unpaired T test. **p < 0.01, ***p < 0.001. B Co-immunoprecipitation analysis of the binding between exogenous Flag-UNC13D and HA-FAK in co-transfected HEK293 cells indicates the direct interaction of them. IgG was incubated with cell lysates as negative controls. C Immunoprecipitation of endogenous FAK from CAPAN-1 and PANC-1 cells confirms the binding between endogenous UNC13D and FAK. D Immunoprecipitation of endogenous RAB11 from PANC-1 overexpressing Flag-UNC13D cells indicates the binding between UNC13D and endogenous RAB11. E Co-immunoprecipitation analysis of the binding among RAB11, UNC13D, and FAK indicates the formation of RAB11-UNC13D-FAK complex. F UNC13D knockdown decreased the binding of RAB11 with FAK. RAB11 was immunoprecipitated from PANC-1 expressing shUNC13D or shSCR to examine the dependency of the interaction between RAB11 and FAK on UNC13D. G Co-localization of FAK, UNC13D, ITGB1, and RAB11 in PANC-1 cells. GFP-FAK, mOrange-UNC13D, and mCerulean-Rab11A cells were transduced. For the active integrin staining, 12G10 anti-ITGB1 was used. The data shown are representative of three independent experiments. Scale bar: 10 μm. H RAB11A knockdown in CAPAN-1 and PANC-1 cells decreased FAK/PXN signaling, which was measured by pFAK, pPaxillin (p-PXN), FAK, and Paxillin (PXN). The quantification of western blotting in (G) is presented as the mean ± SD of three independent experiments. Student’s unpaired T test, **p < 0.01, ***p < 0.001, ****p < 0.0001

Fig. 4

Analysis of the interaction domains of FAK and UNC13D. A Co-immunoprecipitation assay after the transduction of full-length FAK or its truncation mutants in HEK293 cells. Each group was purified by immunoprecipitation with HA beads, followed by a western blot to detect FLAG-UNC13D with the anti-FLAG antibody. B Co-immunoprecipitation analysis after transduction of full-length UNC13D or its truncation mutants in HEK293 cells. Each group was purified by immunoprecipitation with HA beads, followed by a western blot to detect FLAG-UNC13D with the anti-FLAG antibody

Fig. 5

The interaction of UNC13D with FAK is calcium-dependent. A The modulation of calcium-regulated FAK/PXN signaling was measured by the expression level of p-FAK, p-SRC, p-PXN, and p-ERK. The level of calcium was modulated by the treatment with ionomycin 1.25 μM or EGTA 1 mM for 5 min. B The interaction of UNC13D with FAK is modulated by the calcium. The binding between UNC13D and FAK in HEK293 cells was examined by immunoprecipitation after the modulation of calcium concentration by ionomycin 1.25 μM or EGTA 1 mM for 5 min. The quantification data were shown as mean ± SD of three independent experiments. Statistical significance was calculated using a one-way ANOVA with Tukey’s multiple comparison test. * p value < 0.001 (C) Mutations of calcium-binding domains (C2A or C2B) in UNC13D regulated its interaction with FAK. UNC13D wild type or C2 mutants (C2A or C2B) in HEK293 cells were immunoprecipitated with HA beads and immunoblotted by anti-FLAG antibody for the detection of Flag-UNC13D. The quantification data were shown as mean ± SD of three independent experiments. Statistical significance was calculated using a one-way ANOVA with Tukey’s multiple comparison test. ** p value < 0.001 (D) The abstract figure indicating recycling machinery of integrin coupled with FA turnover via RAB11-UNC13D-FAK axis for migration of pancreatic cancer cells. Continuous recycling of integrin via exocytosis and endocytosis of vesicles is required for migration of cancer cells. Through exocytosis of endosomal vesicles, endocytosed integrin reaches at the plasma membrane of leading edge. During the assembly of FA, integrins interact with the extracellular matrix and recruit many proteins including talin, vinculin, paxillin and FAK. During the disassembly of FA, FA complex proteins are disintegrated and integrin is endocytosed into endosomal vesicles in a FAK-dependent manner. During the recycling process of integrin, UNC13D plays roles in tethering and priming of endosomal vesicles to the plasma membrane. Moreover, it can regulate disassembly of FA via RAB11-UNC13D-FAK axis. UNC13D knockdown inhibits exocytosis of endosomal vesicles and disassembly of FA, and finally cellular migration