Evidence that TMEM67 causes polycystic kidney disease through activation of JNK/ERK-dependent pathways

The roles and functions of TMEM protein family members in cancers, cardiovascular and kidney diseases (Review)

Transmembrane protein (TMEM) is a type of membrane proteins, encoded by TMEM gene, also known as integral membrane protein. TMEM gene family contains various members and its encoded proteins have various functions and expressed in numerous organs. It has been proved to be widely involved in the formation of a lot of organelle membranes, enzymes, receptors and channels, mediating numerous normal physiological functions and regulating various disease processes. At present, accumulating evidences at home and abroad have shown that TMEM is involved in regulating the occurrence and development of different tumors, cardiovascular and kidney diseases. The improved understanding of molecular mechanisms of TMEM genes and proteins may provide new directions and ideas for the prevention, diagnosis and treatment of diseases. In the present review, the roles of TMEM and biological functions in various cancers, cardiovascular and kidney diseases were discussed.

Structure of the human Meckel-Gruber protein Meckelin

Mutations in the Meckelin gene account for most cases of the Meckel-Gruber syndrome, the most severe ciliopathy with a 100% mortality rate. Here, we report a 3.3-Å cryo–electron microscopy structure of human Meckelin (also known as TMEM67 and MKS3). The structure reveals a unique protein fold consisting of an unusual cysteine-rich domain that folds as an arch bridge stabilized by 11 pairs of disulfide bonds, a previously uncharacterized domain named β sheet–rich domain, a previously unidentified seven-transmembrane fold wherein TM4 to TM6 are broken near the cytoplasmic surface of the membrane, and a coiled-coil domain placed below the transmembrane domain. Meckelin forms a stable homodimer with an extensive dimer interface. Our structure establishes a framework for dissecting the function and disease mechanisms of Meckelin.

A study of sirolimus and mTOR kinase inhibitor in a hypomorphic Pkd1 mouse model of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (PKD) is characterized by cyst formation and growth, which are partially driven by abnormal proliferation of tubular cells. Proproliferative mechanistic target of rapamycin (mTOR) complexes 1 and 2 (mTORC1 and mTORC2) are activated in the kidneys of mice with PKD. Sirolimus indirectly inhibits mTORC1. Novel mTOR kinase inhibitors directly inhibit mTOR kinase, resulting in the inhibition of mTORC1 and mTORC2. The aim of the present study was to determine the effects of sirolimus versus the mTOR kinase inhibitor torin2 on cyst growth and kidney function in the Pkd1 p.R3277C (Pkd1^RC/RC) mouse model, a hypomorphic Pkd1 model orthologous to the human condition, and to determine the effects of sirolimus versus torin2 on mTORC1 and mTORC2 signaling in PKD1^-/- cells and in the kidneys of Pkd1^RC/RC mice. In vitro, both inhibitors reduced mTORC1 and mTORC2 phosphorylated substrates and negatively impacted cellular metabolic activity, as measured by MTT assay. Pkd1^RC/RC mice were treated with sirolimus or torin2 from 50 to 120 days of age. Torin2 was as effective as sirolimus in decreasing cyst growth and improving loss of kidney function. Both sirolimus and torin2 decreased phosphorylated S6 protein, phosphorylated eukaryotic translation initiation factor 4E-binding protein 1, phosphorylated Akt, and proliferation in Pkd1^RC/RC kidneys. In conclusion, torin2 and sirolimus were equally effective in decreasing cyst burden and improving kidney function and mediated comparable effects on mTORC1 and mTORC2 signaling and proliferation in the Pkd1^RC/RC kidney.

Low expression of TMEM67 is a critical predictor of poor prognosis in human urothelial carcinoma of the bladder

OBJECTIVES

The aim of the study was to evaluate the expression of TMEM67 in urothelial carcinoma of the bladder (UCB) tissues and to determine the potential relevance between the expression of TMEM67 and prognosis of UCB.

MATERIAL AND METHODS

In this study, the expression of TMEM67 mRNA was performed by quantitative real-time PCR in 80 UCB and 54 noncancerous tissues. The expression of TMEM67 protein was identified by immunohistochemistry and western blotting. Chi-square test was conducted to verify the relevance between the expression of TMEM67 and clinical parameters. Kaplan-Meier survival analysis was demonstrated between high or low expression level of TMEM67 mRNA and recurrence-free survival probability. Cox regression analysis was conducted to evaluate the relevance between the expression of TMEM67 and the prognosis in UCB.

RESULTS

Low expression of TMEM67 mRNA and protein was detected in most of UCB tissues using quantitative real-time polymerase chain reaction and western blotting, compared with noncancerous tissues. Low expressions of TMEM67 were associated with TNM stage, grade, and lymph node metastasis (P<0.05). Kaplan-Meier analysis showed that the low expression of TMEM67 mRNA had significantly shorter recurrence-free survival probability (P = 0.018). Cox regression analysis confirmed that low expression of TMEM67 mRNA predicted poor prognosis of patients with UCB (HR = 2.950, P = 0.029, 95% CI: 1.116-7.796).

CONCLUSIONS

TMEM67 expression is low in UCB tissues, and the TMEM67 low expression predicted poor prognosis of patients with UCB.