TMEM16 membrane protein family in health and disease

Mammalian TMEM16 family comprises ten members. Mutations of humanTMEM16 genes have been associated with inherited diseases ranging from bleeding disorder to skeletomuscular disorders and neurological disorders such as dystonia and ataxia. In addition, expression of TMEM16 proteins has been found to be altered in disease conditions such as asthma and certain types of cancers. In 2008, the discoveries of TMEM16A and TMEM16B as the long sought-after calcium-activated chloride channels (CaCCs) greatly stimulated the understandings of these largely uncharacterized proteins. Subsequent studies demonstrated that in addition to CaCCs, the TMEM16 family is also comprised of the calcium-activated non-selective channels and the poorly understood calcium-activated lipid scramblases that can quickly translocate phospholipids from one leaflet to the other and destroy their asymmetric distribution on cell membranes in a calcium-dependent manner. Our laboratory aims to understand the biology of TMEM16 proteins at molecular, cellular and system levels using a combination of mouse genetics, biophysical, biochemical and novel imaging approaches. 

Structure-Function of TMEM16 proteins

We are interested in understanding three basic properties of TMEM16 proteins: substrate selectivity, activation mechanism and pharmacology. (1) We have shown that instead of being a CaCC, TMEM16F forms a Small-conductance, Calcium-Activated Nonselective (SCAN) channel. Recent studies also suggest that TMEM16F may serve as a calcium-activated lipid scramblase. We will study how TMEM16 proteins selectively transport ions and phospholipids. (2) We identified the calcium binding sites in the TMEM16A-CaCC, which are highly conserved among TMEM16 proteins. We will study how TMEM16 ion channels and lipid scramblases are activated by calcium and other stimuli. (3) We demonstrated that the TMEM16 channels have different pharmacological profiles. We will understand the molecular basis of TMEM16 pharmacology and screen specific and potent pharmacological modulators for TMEM16 proteins.

Physiology of TMEM16 proteins

TMEM16 proteins are expressed in different cell types, including neurons, muscle cells, blood cells, immune cells and epithelial cells. Their physiological and pathological roles remain to be established. We are working on understanding the assembly, trafficking, activation, regulation and function of TMEM16 channels and lipid scramblases in neurons, muscle cells and blood cells. We are also interested in understanding the roles of TMEM16 proteins in cancers. In order to study and manipulate the TMEM16 ion channels and lipid scramblases in various cell types, we will apply and develop molecular sensors and actuators that can monitor and control TMEM16 protein activities in vitro and in vivo. In addition, we will combine mouse genetics, mouse behavioral tests and novel in vivo imaging tools to illustrate the functions of the TMEM16 proteins in the brain. 

What are Ion Channels?

Ion channels are pore-forming membrane proteins that allow the passive transport of ions through hydrophobic core of the membranes of virtually all living cells. They are special enzymes that catalyze the ion transport at high speed, with exquisite specificity and under very tight regulation. The flow of ions down their transmembrane electrochemical gradient changes the net charge of a cell and thereby changes its membrane voltage, which ultimately controls responses specific to cellular context.

Physiological Roles of  Ion Channels.

Ion channels are fundamental to cellular existence - from simple bacteria to highly specialized neurons. In unicellular organisms, ion channels help maintain the volume, the homeostasis of inorganic ions and the generation of Ca2+ transients, which are important in many key cellular events, including secretion, gene expression and cell division. In multicellular organisms, ion channels play much more sophisticated roles. They are essential components to generate electrical signals. These electrical signals and the resulting intracellular Ca2+ transients transmit information among cells and tissues over long distance with high speed and fidelity, tightly coordinating distant cellular functions. Therefore, ion channels are important in many physiological processes, including muscle contraction, hormone secretion, sensation and mental processes. If the function of ion channels goes wrong, there can be serious consequences, including life-threatening diseases, such as epilepsy, cardiac arrhythmia, hypertension, cystic fibrosis, diabetes and cancer.

TMEM16 Family

Asymmetric distribution of membrane lipids.

In eukaryotic cells, phospholipids on the plasma membrane are asymmetrically distributed with phosphatidylcholine (PC) and sphingomyelin (SPH) predominantly residing in the outer leaflet, whereas the aminophospholipids phosphatidylethanolamine (PE) and phosphatidylserine (PS) are enriched in the inner leaflet. 

How is the membrane lipid asymmetry established?

This asymmetry is delicately maintained by two types of ATP-driven lipid translocases: flippases and floppases actively catalyze the trans-bilayer movement of PS/PE to the inner leaflet and PC/SPH to the outer leaflet, respectively. 

What are lipid scramblases?

Under certain physiological conditions such as platelet activation, neurotransmitter release, sperm capacitation or apoptosis, a third type of lipid translocase called scramblases can be activated, which rapidly and nonselectively flip-flop all phospholipid species. Different from flippases and floppases, the activation of lipid scramblases does not require ATP hydrolysis. Instead, elevation of intracellular calcium or activation of caspase cascades during apoptosis can activate scramblases. Recent studies from the Nagata group suggest that TMEM16F and Xkr8 are responsible for the calcium-activated and apoptosis-induced lipid scrambling, respectively. 

What are the consequences of lipid scrambling?

Lipid composition asymmetry defines the physical and chemical properties of the plasma membrane, as well as its interactions with intracellular and extracellular molecules. Scrambling of lipid species destroys membrane lipid asymmetry and results in the exposure of the negatively charged PS to the cell surface. PS exposure has been shown to be important in various physiological processes such as platelet activation, apoptosis, neurotransmitter release and sperm capacitation. For instance, the exposed PS in platelets serves as a platform to recruit key factors to convert prothrombin to thrombin, a key step in the blood clotting cascade. On the other hand, the exposed PS in apoptotic cells can serve as an “eat-me” signal to attract phagocytes to clean the post-apoptotic cell corpses.

Dong, Ping, Yang Zhang, Arsen S. Hunanyan, Mohamad A. Mikati, Jianmin Cui, and Huanghe Yang. “Neuronal mechanism of a BK channelopathy in absence epilepsy and dyskinesia.” Proc Natl Acad Sci U S A 119, no. 12 (March 22, 2022): e2200140119. https://doi.org/10.1073/pnas.2200140119.

Chen, Yong, Zi-Long Wang, Michele Yeo, Qiao-Juan Zhang, Ana E. López-Romero, Hui-Ping Ding, Xin Zhang, et al. “Epithelia-Sensory Neuron Cross Talk Underlies Cholestatic Itch Induced by Lysophosphatidylcholine.” Gastroenterology 161, no. 1 (July 2021): 301-317.e16. https://doi.org/10.1053/j.gastro.2021.03.049.

Liang, Pengfei, and Huanghe Yang. “Molecular underpinning of intracellular pH regulation on TMEM16F.” J Gen Physiol 153, no. 2 (February 1, 2021). https://doi.org/10.1085/jgp.202012704.

Le, Son C., Pengfei Liang, Augustus J. Lowry, and Huanghe Yang. “Gating and Regulatory Mechanisms of TMEM16 Ion Channels and Scramblases.” Front Physiol 12 (2021): 787773. https://doi.org/10.3389/fphys.2021.787773.

Le, Son C., and Huanghe Yang. “Structure-Function of TMEM16 Ion Channels and Lipid Scramblases.” Adv Exp Med Biol 1349 (2021): 87–109. https://doi.org/10.1007/978-981-16-4254-8_6.

Le, Son C., and Huanghe Yang. “An Additional Ca2+ Binding Site Allosterically Controls TMEM16A Activation.” Cell Rep 33, no. 13 (December 29, 2020): 108570. https://doi.org/10.1016/j.celrep.2020.108570.

Liao, Chengheng, Yang Zhang, Cheng Fan, Laura E. Herring, Juan Liu, Jason W. Locasale, Mamoru Takada, et al. “Identification of BBOX1 as a Therapeutic Target in Triple-Negative Breast Cancer.” Cancer Discov 10, no. 11 (November 2020): 1706–21. https://doi.org/10.1158/2159-8290.CD-20-0288.

Zhang, Guohui, Rebecca A. Gibson, Marie McDonald, Pengfei Liang, Po Wei Kang, Jingyi Shi, Huanghe Yang, Jianmin Cui, and Mohamad A. Mikati. “A Gain-of-Function Mutation in KCNMA1 Causes Dystonia Spells Controlled With Stimulant Therapy.” Mov Disord 35, no. 10 (October 2020): 1868–73. https://doi.org/10.1002/mds.28138.

Le, Trieu, Son C. Le, Yang Zhang, Pengfei Liang, and Huanghe Yang. “Evidence that polyphenols do not inhibit the phospholipid scramblase TMEM16F.” J Biol Chem 295, no. 35 (August 28, 2020): 12537–44. https://doi.org/10.1074/jbc.AC120.014872.

Zhang, Yang, Trieu Le, Ryan Grabau, Zahra Mohseni, Hoejeong Kim, David R. Natale, Liping Feng, Hua Pan, and Huanghe Yang. “TMEM16F phospholipid scramblase mediates trophoblast fusion and placental development.” Sci Adv 6, no. 19 (May 2020): eaba0310. https://doi.org/10.1126/sciadv.aba0310.

Department of Biochemistry/Ion Channel Research Unit
Duke University School of Medicine

Telephone:
Lab:      919-681-0175
Office:  919-684-1406
Fax:      919-613-5145

Mailing Address:
Box 103030, DUMC
Durham, NC 27710

Physical Address:
2 Genome Ct,
MSRB2 Building, Room 2100E (Lab)
MSRB2 Building, Room 2017 (Office)
Durham, NC 27710

Positions

We’re always looking for talented, motivated scientists of any level to join us. 

Postdoctoral fellows

Please e-mail Huanghe at huanghe.yang@duke.edu with your CV, a short description about your background, your major contributions and interest in our lab.

Graduate students

This lab is affiliated with several Duke graduate programs and may accept rotation at any time of year. Please contact Huanghe at huanghe.yang@duke.edu to discuss a potential rotation. 

Undergraduates

Please send an e-mail with a short note about your interest in our lab, your CV, and a transcript to Huanghe at huanghe.yang@duke.edu.

Staff

An opening to lab technician is currently available in the lab. Candidates please e-mail Huanghe at huanghe.yang@duke.edu with your CV and a brief description of your background, experience and skills.