Mer is one member of Axl receptor tyrosine kinase family, and its ligand Gas6 can stimulate activity of Mer receptor tyrosine kinase after binding it, and then activate the downstream signal transduction pathway, Mer participates in cell inflammation, apoptosis, tumorigenesis, thrombosis and hemostasis. Rencet advances of study on Mer function were reviewed, and its potential prospects of antithrombosis and antitumor were discussed in this article.
Animals ; Fibrinolytic Agents ; Humans ; Intercellular Signaling Peptides and Proteins ; metabolism ; Proto-Oncogene Proteins ; genetics ; metabolism ; Receptor Protein-Tyrosine Kinases ; genetics ; metabolism ; Signal Transduction ; c-Mer Tyrosine Kinase

BACKGROUNDMüller cells in the mammalian retina normally express low levels of glial fibrillary acidic protein (GFAP); however, its expression is upregulated in response to the loss of retinal neurons. The change in expression of GFAP is one of the earliest indicators of retinal damage and is correlated with the time course of disease. The aim of this study was to investigate the time course of degeneration and the expression of GFAP in the retina of mer knockout mice.

METHODSA total of 30 mer knockout mice, aged from 15 - 20 days to 1 year and 32 age-matched wild type mice as controls were tested. Immunohistochemistry was used to show the expression of GFAP in the central and peripheral retina of mer knockout and control mice at postnatal age of 15 days (P15d), 20 days (P20d), 4 weeks (P4w), 6 weeks (P6w), 8 weeks (P8w), 3 months (P3m), 6 months (P6m) and 1 years (P1y).

RESULTSThe expression of GFAP in the central and peripheral retina of wild type mice was limited to the retinal ganglion cell and nerve fiber layers. In the central retina of mer knockout mice, GFAP expression was upregulated at P4w and GFAP immunolabelling penetrates across the entire thickness of the retina at P8w; whereas in the peripheral retina, the GFAP expression was upregulated at P20d and GFAP immunolabelling penetrates the entire retina after P4w.

CONCLUSIONSIncreased expression of GFAP in Müller cells of mer knockout mice occur at P20d in the peripheral retina and P4w in the central retina. GFAP expression in Müller cells appears to be a secondary response to the loss of retinal neurons. Increased expression of GFAP may occur prior to any detectable morphological changes in the retina. This study suggests that the loss of retinal neurons may begin in the early stages of retinitis pigmentosa, prior to the discovery of any morphological changes in the retina.

Animals ; Glial Fibrillary Acidic Protein ; metabolism ; Immunohistochemistry ; Mice ; Mice, Knockout ; Proto-Oncogene Proteins ; genetics ; Receptor Protein-Tyrosine Kinases ; genetics ; Retina ; metabolism ; pathology ; Retinitis Pigmentosa ; genetics ; metabolism ; c-Mer Tyrosine Kinase

Objective: PD-1/PD-L1 immune checkpoint treatment is effective for some triple-negative breast cancer populations with PD-L1 expression, but the response rate is still not satisfactory. This study aims to explore the mechanism of drug resistance to breast cancer anti-PD-1 therapies and the strategies for overcoming the resistance to PD-1therapies. Methods: By constructing a human triple-negative breast cancer drug-resistant cell line called BT-549R5 and a mouse breast cancer drug-resistant cell line called 4T1R3, and applying the whole-gene shRNA library screening, candidate drug resistance-associated molecules were obtained and verified by cytological experiments. The expression of Tyro3, Axl and MerTK of the TAM family in the 4T1R3 group was tested using the Western blot method. The down-regulation of CDK9 on the effect of T cells killing the BT-549R5 cells was observed through T cell killing tests, while the down-regulation of Tyro3 and CDK9 on the effect of anti-PD-1 therapies for transplanted breast tumors was observed in mouse tumor formation experiments. Results: The cell lines and animal models of breast cancer resistant to PD-1 treatment were successfully constructed. Tyro3, Axl and MerTK were highly expressed in 4T1R3 cells. Whole genome sequencing showed that Tyro3 and CDK9 were highly expressed in BT-549R5 cells. T cell killing experiment showed that the survival rate of BT-549R5 cells in the CDK9 down-regulated group and the control group decreased gradually with the increase of T cells, but the survival rate of BT-549R5 cells in the CDK9 down-regulated group decreased rapidly. Tumor formation experiment in mice showed that under anti-PD-1 treatment, the transplanted tumor in the 4T1R3 cell group grew rapidly compared with the 4T1 cell group (P<0.05), and the tumor volume of the 4T1R3 group was larger than that of the 4T1 group on Day 20. Nevertheless, the tumor growth rates in the CDK9-knockdown 4T1R3 cell group and the Tyro3-knockdown 4T1R3 cell group were similar to that of the 4T1 cell group, and the tumor volumes at day 20 were signiference lower than that of 4T1R3 cell group(P<0.05). Conclusions: Tyro3 and CDK9 are associated with the drug resistance to anti-PD-1 therapies for breast cancer. Inhibiting the expression of Tyro3 and CDK9 can reverse the drug resistance to breast cancer treatment.
Humans ; Animals ; Mice ; c-Mer Tyrosine Kinase/metabolism* ; Receptor Protein-Tyrosine Kinases/genetics* ; Axl Receptor Tyrosine Kinase ; Proto-Oncogene Proteins/metabolism* ; B7-H1 Antigen/genetics* ; Triple Negative Breast Neoplasms/genetics* ; Drug Resistance, Neoplasm ; Biomarkers ; Cell Line, Tumor ; Cyclin-Dependent Kinase 9

Objective: PD-1/PD-L1 immune checkpoint treatment is effective for some triple-negative breast cancer populations with PD-L1 expression, but the response rate is still not satisfactory. This study aims to explore the mechanism of drug resistance to breast cancer anti-PD-1 therapies and the strategies for overcoming the resistance to PD-1therapies. Methods: By constructing a human triple-negative breast cancer drug-resistant cell line called BT-549R5 and a mouse breast cancer drug-resistant cell line called 4T1R3, and applying the whole-gene shRNA library screening, candidate drug resistance-associated molecules were obtained and verified by cytological experiments. The expression of Tyro3, Axl and MerTK of the TAM family in the 4T1R3 group was tested using the Western blot method. The down-regulation of CDK9 on the effect of T cells killing the BT-549R5 cells was observed through T cell killing tests, while the down-regulation of Tyro3 and CDK9 on the effect of anti-PD-1 therapies for transplanted breast tumors was observed in mouse tumor formation experiments. Results: The cell lines and animal models of breast cancer resistant to PD-1 treatment were successfully constructed. Tyro3, Axl and MerTK were highly expressed in 4T1R3 cells. Whole genome sequencing showed that Tyro3 and CDK9 were highly expressed in BT-549R5 cells. T cell killing experiment showed that the survival rate of BT-549R5 cells in the CDK9 down-regulated group and the control group decreased gradually with the increase of T cells, but the survival rate of BT-549R5 cells in the CDK9 down-regulated group decreased rapidly. Tumor formation experiment in mice showed that under anti-PD-1 treatment, the transplanted tumor in the 4T1R3 cell group grew rapidly compared with the 4T1 cell group (P<0.05), and the tumor volume of the 4T1R3 group was larger than that of the 4T1 group on Day 20. Nevertheless, the tumor growth rates in the CDK9-knockdown 4T1R3 cell group and the Tyro3-knockdown 4T1R3 cell group were similar to that of the 4T1 cell group, and the tumor volumes at day 20 were signiference lower than that of 4T1R3 cell group(P<0.05). Conclusions: Tyro3 and CDK9 are associated with the drug resistance to anti-PD-1 therapies for breast cancer. Inhibiting the expression of Tyro3 and CDK9 can reverse the drug resistance to breast cancer treatment.
Humans ; Animals ; Mice ; c-Mer Tyrosine Kinase/metabolism* ; Receptor Protein-Tyrosine Kinases/genetics* ; Axl Receptor Tyrosine Kinase ; Proto-Oncogene Proteins/metabolism* ; B7-H1 Antigen/genetics* ; Triple Negative Breast Neoplasms/genetics* ; Drug Resistance, Neoplasm ; Biomarkers ; Cell Line, Tumor ; Cyclin-Dependent Kinase 9

OBJECTIVETo explore anti-angiogenesis effect of Mer, a member of tyrosine kinase receptor family, and its mechanism.

METHODSHuman Mer full length plasmid was transfected into HMEC-1 cells through liposome. G418 was used to select positive clone. Expression of Mer at mRNA and protein level was detected by real-time PCR and Western-blot, respectively. Transwell and Matrigel were used to evaluate the effect of overexpressed Mer on migration and angiogenesis of HMEC-1 cells. Primary angiogenesis associated factor VEGF-A, VEGF-B, VEGF-C, VEGF-D and VEGFR-1, VEGFR-2 were screened by real-time PCR.

RESULTSAfter G418 selection, the Mer expression in transfected HMEC-1 cells was increased 3.61- and 2.12 fold at mRNA and protein level, respectively. Compared with negative control, the migration of Mer-HMEC-1 was decreased (21 +/- 6 vs 36 +/- 11), and angiogenesis capability on Matrigel significantly decreased. By real-time PCR, the expression of VEGF-C and VEGFR-2 was down-regulated to 44.7% and 25.6% of the negative control.

CONCLUSIONOverexpressed Mer tyrosine kinase receptor can inhibit the migration and angiogenesis of HMEC-1 cells through VEGF-C/VEGFR-2 signal pathway.

Cell Line ; Cell Movement ; Cell Proliferation ; Endothelial Cells ; metabolism ; physiology ; Endothelium, Vascular ; cytology ; Humans ; Neovascularization, Physiologic ; Proto-Oncogene Proteins ; genetics ; metabolism ; RNA, Messenger ; metabolism ; Receptor Protein-Tyrosine Kinases ; genetics ; metabolism ; Receptors, Vascular Endothelial Growth Factor ; metabolism ; Transfection ; Vascular Endothelial Growth Factors ; metabolism ; c-Mer Tyrosine Kinase

BACKGROUNDStudies indicated that Mer might be the main contributor to the specific internalization of photoreceptor outer segments (POS) in retinal pigment epithelium (RPE). It is very important to understand the mechanism of POS phagocytosis under the pathway of Mer and its ligands. The objective of this study was to identify changes in gene expression profiles caused by Mer gene knockout (Mer-/-) during phagocytosis of POS in RPE.

METHODSRPE from both Mer-/- and wild-type (WT) mice were isolated and cultured to the 3rd passage. POS were subjected to culture medium with 20 nmol/L Gas6 and protein S to activate specific mer-mediated phagocytosis. RPE phagocytosis was evaluated by phagocytosis assays and differential gene expression identified by microarray at 3 and 12 hours; the 0-hour time point served as the control. Three independent samples for each Mer-/- or WT RPE were subjected to the same protocol of microarray. Five genes were confirmed by real-time quantitative PCR (QPCR).

RESULTSThe Mer-/- RPE had less internalized POS than WT RPE after both 3 and 12 hours in phagocytosis assay. Compared to WT RPE and the 0-hour control, 38 and 45 different known genes were increased and 68 and 59 known genes were decreased in Mer-/- RPE after 3 and 12 hours, respectively. Abnormal POS phagocytosis in Mer-/- RPE was associated with significant gene expression changes in, for example, signal transduction (WNT, MAPK), phagocytosis (Vav3, Hsd11b1), cytoskeleton components (Myo7a), and metabolism, in a time-specific manner. QPCR results showed Vav3, Hsd11b1, Myo7a, Rtn2 and Itga8 in those independent samples were consistent with microarray.

CONCLUSIONGene expression profiles modulated in a time-specific manner in Mer-/- RPE indicate a possible internalization mechanism for abnormal POS phagocytosis, which gives insight into the mechanism of retinitis pigmentosa caused by the mutation of MerTK in humans.

Animals ; Gene Expression Profiling ; Mice ; Mice, Knockout ; Mice, Mutant Strains ; Oligonucleotide Array Sequence Analysis ; Phagocytosis ; genetics ; physiology ; Proto-Oncogene Proteins ; genetics ; metabolism ; Receptor Protein-Tyrosine Kinases ; genetics ; metabolism ; Retinal Pigment Epithelium ; cytology ; Reverse Transcriptase Polymerase Chain Reaction ; Tissue Culture Techniques ; c-Mer Tyrosine Kinase