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Unmasking the "Foreman" Of The Golgi Apparatus

August 05, 2004

The cell is a highly organized factory where each constituent has its place and a role to play. If one piece of this machinery falters, the whole cell is imperiled. The least anomaly may result in an uncontrolled cell likely to engender a variety of diseases, such as cancers.

At the Institut Curie, CNRS researchers, in collaboration with a group at the University of Seville, have just shown that the protein GMAP-210 is the "foreman" essential to maintenance of the integrity and localization of the Golgi apparatus at the heart of the cell. This discovery, published in the August 6 issue of Cell, should enhance our understanding of how the cellular machinery works.

The cell is a miniature factory full of "machines" each with its own precise role to play: the endoplasmic reticulum(1) produces the linchpins of the cell, proteins. The Golgi apparatus (see box opposite) modifies, sorts and assigns them their tasks. Mitochondria supply energy. The cytoskeleton forms the cell's backbone and ensures the movements of the different cell components.
To be "operational", these little machines are constantly "exerting" themselves: they fulfill their function, interact, communicate, keep an eye on each other. In reality, cellular stability masks a hive of activity. This constant cellular activity demands great reliability since if an anomaly arises and persists, the whole cell may be endangered. The least malfunction of the cogwheels of the cellular machinery may give rise to defective cells likely to give rise to various diseases, including cancers.

The Golgi apparatus: eternal renewal
The team of Michel Bornens(2) at the Institut Curie, in collaboration with the group of Rosa Rios at the University of Seville(3), is studying the dynamics of the Golgi apparatus which, like other cellular machinery, works "round the clock".
In addition to its task marshalling proteins, the Golgi apparatus renews itself three to four times per cell cycle. These two operations are underpinned by permanent communication between the Golgi apparatus and the endoplasmic reticulum. The latter supplies both the proteins which transit the Golgi apparatus on their way to their destinations and pre-Golgi structures that serve to renew the Golgi apparatus. These pre-Golgi elements are constantly transported from the endoplasmic reticulum via the network of microtubules(1) which leads to the centrosome(1) - the "geographical" center of the cell -, and ensure that the Golgi apparatus remains functional.
The researchers have just discovered that protein GMAP-210 acts as a "clamp", holding these future components of the Golgi apparatus close to the center of the cell to enable their assembly. To this end, the protein controls the formation of a short microtubule, which brings together and juxtaposes these pre-Golgi structures.
The scientists have observed that the Golgi apparatus fragments when GMAP-210 is inactivated. In contrast, if GMAP-210 abounds, the Golgi grows ceaselessly and may even divide.
It has therefore been shown that GMAP-210 plays an essential role in "maintaining" the Golgi apparatus and in positioning it in the center of the cell. Such upkeep and positioning are essential to the correct functioning of the cell, and on a larger scale to the organism as a whole. GMAP-210 was, moreover, identified because of its involvement in an auto-immune disease(4) and in certain leukemias.
The Golgi apparatus is also "renewed" at each cell division from its own fragments, which presupposes a role for GMAP-210 in this crucial step (see box below).

The discovery of the key role of GMAP-210 heightens understanding of how the cell preserves its integrity throughout its life. Continued studies should cast light on other unsolved questions concerning the mechanisms indispensable to good functioning of the cell and indeed of the whole body.

Institut Curie