Role of the endomembrane system in lysosome biogenesis
Abstract
The objective of this research was to define the pathways followed in rat liver by lysosomal constituents during processing and transport to the lysosome and more specifically the involvement of the Golgi apparatus in that process. Biochemical and immunological analyses of membrane fractions revealed lysosomal enzyme activities ($\beta$-glucuronidase, $\beta$-hexosaminidase and acid phosphatase) throughout the rough endoplasmic reticulum and Golgi apparatus as well as in lysosomes. The phosphomannosyl receptor was localized to the rough endoplasmic reticulum, rough-smooth transitional elements associated with the endoplasmic reticulum, and to the Golgi apparatus and in Golgi apparatus subfractions enriched in cis and trans cisternae. Immunoprecipitation of lysosomal constituents showed localization in endoplasmic reticulum and Golgi apparatus fractions. The receptor as well as lysosomal enzymes was found in cis and trans Golgi apparatus subfractions. In contrast, results from the immunocytochemistry showed both $\beta$-glucuronidase and the phosphomannosyl receptor to be localized in a tubular system in association with the Golgi apparatus and in the lysosomes. This tubular system is not synonymous with the GERL or the trans Golgi reticulum nor is it the tubular system of the boulevard peripherique of lipoprotein transport. It represents yet a new structure hitherto unrecognized that is peripheral to the Golgi apparatus rather than trans. The immunocytochemical localization of the lysosomal enzyme and the phosphomannosyl receptor would agree with the biochemical localization if the tubular system of the lysosomal enzyme delivery were isolated along with the Golgi apparatus cisternae. The results suggest that lysosomal constituents do not traverse the Golgi apparatus complex but rather move from the endoplasmic reticulum to lysosomes directly via a tubular system associated with the Golgi apparatus periphery and enter the Golgi apparatus nearly exclusively at the trans face. As such, the initial site of separation/sorting of lysosomal constituents from secretory proteins would be at the endoplasmic reticulum and not the Golgi apparatus as is currently widely accepted.
Degree
Ph.D.
Advisors
Morre, Purdue University.
Subject Area
Biology
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