Milk biosynthesis requires the Golgi cation exchanger TMEM165

Abstract

Milk is a hallmark of mammals that is critical for normal growth and development of offspring. During biosynthesis of lactose in the Golgi complex, H ؉ is produced as a by-product, and there is no known mechanism for maintaining luminal pH within the physiological range. Here, using conditional, tissuespecific knockout mice, immunostaining, and biochemical assays, we test whether the putative H ؉ /Ca 2؉ /Mn 2؉ exchanger known as TMEM165 (transmembrane protein 165) participates in normal milk production. We find TMEM165 is crucial in the lactating mammary gland for normal biosynthesis of lactose and for normal growth rates of nursing pups. The milk of TMEM165-deficient mice contained elevated concentrations of fat, protein, iron, and zinc, which are likely caused by decreased osmosis-mediated dilution of the milk caused by the decreased biosynthesis of lactose. When normalized to total protein levels, only calcium and manganese levels were significantly lower in the milk from TMEM165-deficient dams than control dams. These findings suggest that TMEM165 supplies Ca 2؉ and Mn 2؉ to the Golgi complex in exchange for H ؉ to sustain the functions of lactose synthase and potentially other glycosyl-transferases. Our findings highlight the importance of cation and pH homeostasis in the Golgi complex of professional secretory cells and the critical role of TMEM165 in this process. . 3 The abbreviations used are: TMEM165, transmembrane protein 165;␤4-GALT-I, ␤4-galactosyltransferase I; SPCA, secretory pathway Ca 2ϩ / Mn 2ϩ -ATPase; WAP, whey acid protein; ICP, inductively coupled plasma; TUNEL, terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling.

A Comparative Review of the Cell Biology, Biochemistry, and Genetics of Lactose Synthesis

“…For example, hydrogen protons are a byproduct of glycosylation, where the Ca 2+/ Mn 2+ ATPase 1, TMEM165, works as a hydrogen exchanger to deacidify the Golgi. In keeping with this critical function for TMEM165, its conditional deletion in the mammary glands decreased LS activity and milk lactose content by 36% [95]. Likewise, a high concentration of K inhibited LS activity in vitro, but only in the concentration range at which potassium was bound to LALBA [79].…”

From the Uncharacterized Protein Family 0016 to the GDT1 family: Molecular insights into a newly-characterized family of cation secondary transporters

“…According to this latter statement, Gdt1p would be a putative actor in eliminating the proton load generated by glycosylation, in exchange of transport of divalent cations from the cytosol to the Golgi [ 28 ]. In the same line, the increased expression of TMEM165 during lactation might reflect its role in providing the Golgi lumen of lactating mammary cells with Ca 2+ as nutrient and Mn 2+ as cofactor of enzymes, but also in removing the protons generated as by-product of lactose production out of the Golgi lumen [ 26 , 53 ]. Since there are no clear proton export mechanisms from the Golgi to now both in yeast and human, this involvement of the UPF0016 members in Golgi pH homeostasis appears as highly interesting for further investigation in the near future.…”

The Mechanism of Zinc Sulfate in Improving Fertility in Obese Rats Analyzed by Sperm Proteomic Analysis

“…However, data obtained in recent study give several indications of their implication in calcium and manganese homeostasis [47]. TM165 supplies Ca2+ and Mn2+ to the Golgi complex in exchange for H+ to sustain the functions of lactose synthase and potentially other glycosyltransferases [48,49]. The human Golgi protein TM165 can transport calcium and manganese in yeast and bacterial cells [50].…”