Microtubules are important in maintaining the structure of the cell, holding organelles in place and allowing for control of movement. Kinesins, on the microtubules, hold the Golgi, mitochondria, and endoplasmic reticulum in place, allowing the control of protein localisation (as the Golgi and ER are both involved in localising proteins).
Disrupting microtubules, by drugs (such as colchicine) or otherwise, prevents the Golgi, ER, and mitochondria from being held in place. This impairs the cell’s ability to transport proteins, and causes the Golgi to collapse as well as mitochondria beginning to wander. By diminishing the ability of the cell to control the movement of organelles, it is no longer possible to transport proteins specifically.