# Involvement of GTPases and vesicle adapter proteins in Heparan sulfate biosynthesis: role of Rab1A, Rab2A and GOLPH3

## TL;DR

This study shows how Rab1A, Rab2A, and GOLPH3 regulate heparan sulfate production through vesicle trafficking in the Golgi, maintaining enzyme localization and sulfation balance.

## Contribution

The study reveals a compensatory relationship between Rab1A and Rab2A and identifies GOLPH3's role in COPI vesicle-mediated enzyme transport during heparan sulfate biosynthesis.

## Key findings

- Rab1A silencing shifts 3OST5 to the trans-Golgi, increasing HS levels within 24–48 h.
- Rab2A silencing causes 3OST5 to accumulate in the cis-Golgi with delayed HS increase and upregulates Rab1A.
- GOLPH3 facilitates COPI vesicle trafficking of 3OST5, influencing HS biosynthesis.

## Abstract

Vesicle trafficking is pivotal in heparan sulfate (HS) biosynthesis, influencing its spatial and temporal regulation within distinct Golgi compartments. This regulation modulates the sulfation pattern of HS, which is crucial for governing various biological processes. Here, we investigate the effects of silencing Rab1A and Rab2A expression on the localisation of 3‐O‐sulfotransferase‐5 (3OST5) within Golgi compartments and subsequent alterations in HS structure and levels. Interestingly, silencing Rab1A led to a shift in 3OST5 localization towards the trans‐Golgi, resulting in increased HS levels within 24 and 48 h, while silencing Rab2A caused 3OST5 accumulation in the cis‐Golgi, with a delayed rise in HS content observed after 48 h. Furthermore, a compensatory mechanism was evident in Rab2A‐silenced cells, where increased Rab1A protein expression was detected. This suggests a dynamic interplay between Rab1A and Rab2A in maintaining the fine balance of vesicle trafficking processes involved in HS biosynthesis. Additionally, we demonstrate that the trafficking of 3OST5 in COPI vesicles is facilitated by GOLPH3 protein. These findings identify novel vesicular transport mechanisms regulating HS biosynthesis and reveal a compensatory relationship between Rab1A and Rab2A in maintaining baseline HS production.

Vesicle trafficking governs the biosynthesis of heparan sulfate (HS) by controlling the positioning of HS‐modifying enzymes within Golgi compartments. The proteins Rab1A and Rab2A play dynamic, compensatory roles that affect HS levels by influencing the transport of these enzymes. GOLPH3 facilitates the COPI vesicle‐mediated transport of HS‐modifying enzymes, revealing new mechanisms and interactions vital for maintaining balanced HS production, which is crucial for cellular functions.