ATG8-interacting (ATI) 1 and 2 define a plant starvation-induced ER-phagy pathway and serve as MSBP1 (MAPR5) cargo-receptors

ER-phagy, the selective autophagy of endoplasmic reticulum (ER) components, is known to operate in eukaryotes from yeast and unicellular algae to animals and plants. Thus far, only ER-stress derived ER-phagy was reported and analyzed in plants. In this study we characterize an ER-phagy pathway in Arabidopsis thaliana that is triggered by dark-induced starvation and not by ER-stress. This pathway is defined by the previously reported ATG8-interacting proteins, ATI1 and ATI2 and is regulated by the TOR signaling pathway. We further identified ER-localized Membrane Steroid Binding Protein 1 (MSBP1) as an ATI1 and 2 interacting protein and an autophagy cargo, and show that ATI1 and 2 serve as its cargo receptors. Together, these findings expand our knowledge on plants responses during energy deprivation and highlight the role of this special type of ER-phagy in this process.

Biochemistry, pharmacology and physiological role of sex hormone binding globulin

Sex steroid binding protein (SBP) is a plasma protein that specifically binds sex steroids with high affinity. It is synthesized in the liver and circulates in the plasma of many species including human, monkey, cattle, dog, cat and others. SBP is a dimeric protein with a Mr ranging between 84-9Θ KDa and binds one steroid molecule per dimer. Its expression is regulated by many hormones and estradiol promotes while testosterone inhibits its expression. Its physiological role is not known completely, but it is likely to control at least the bioavailable levels of circulating steroids. Experimental evidence from our laboratory and others supports the dogma that non-bound steroids are free to enter the target cells and act. After the discovery of SBP-membrane receptor, it seems that SBP serves also other biological role except that of binding steroids. All recent reports are discussed.