Title : Exosome-related multi-pass transmembrane protein TSAP6 is a target of rhomboid protease RHBDD1-induced proteolysis
Abstract :
We have previously reported that rhomboid domain containing 1 ( RHBDD1 ), a mammalian rhomboid protease highly expressed in the testis, can cleave the Bcl-2 protein Bik
In this study, we identified a multi-pass transmembrane protein , tumor suppressor activated pathway-6 ( TSAP6 ) as a potential substrate of RHBDD1
RHBDD1 was found to induce the proteolysis of TSAP6 in a dose- and activity-dependent manner
The cleavage of TSAP6 was not restricted to its glycosylated form and occurred in three different regions
In addition, mass spectrometry and mutagenesis analyses both indicated that the major cleavage site laid in the C-terminal of the third transmembrane domain of TSAP6
A somatic cell knock-in approach was used to genetically inactivate the endogenous RHBDD1 in HCT116 and RKO colon cancer cells
Exosome secretion was significantly elevated when RHBDD1 was inactivated in the two cells lines
The increased exosome secretion was verfied through the detection of certain exosomal components, including Tsg101 , Tf-R , FasL and Trail
In addition, the elevation of exosome secretion by RHBDD1 inactivation was reduced when TSAP6 was knocked down, indicating that the role of RHBDD1 in regulating exosomal trafficking is very likely to be TSAP6-dependent
We found that the increase in FasL and Trail increased exosome-induced apoptosis in Jurkat cells
Taken together, our findings suggest that RHBDD1 is involved in the regulation of a nonclassical exosomal secretion pathway through the restriction of TSAP6