Abstract
The authors of the accompanying classic paper from the Journal of Histochemistry and Cytochemistry (Evanko SP, Wight TN. Intracellular Localization of Hyaluronan in Proliferating Cells. Journal of Histochemistry & Cytochemistry. 1999;47[10]:1331–1341) comment on the impact and significance of their findings on the intracellular localization of hyaluronan in arterial smooth muscle cells using immunohistochemical techniques. These seminal findings signaled the potential for a role of hyaluronan in the functions of microtubules and mitosis.
This study arose in somewhat of a serendipitous fashion resulting from our interest in identifying whether certain components of the extracellular matrix (ECM) such as hyaluronan (HA) influenced the ability of cells to undergo division and migration (reviewed by Evanko et al.). 1 Using established histochemical protocols for identifying HA in cell cultures, we found that HA increased dramatically outside cells when cultured arterial smooth muscle cells were stimulated to divide and migrate. It was clear also that HA was associated with cell surfaces and parts inside cells. Using chromogenic substrates or fluorescent-tagged secondary reagents, we found HA in the nucleus, specifically the nucleolus, and in vesicles in the cytoplasm. The cytoplasmic vesicles partially colocalize with lysosomal markers and contain internalized HA in various stages of degradation. These results extended previous biochemical and electron microscopic observations of HA inside cells, which date back to the 1980s or earlier. 2 This finding stimulated additional studies which demonstrated that intracellular HA was associated with organelles such as microtubules prominent in the mitotic spindle and the microtubule-binding HA receptor, RHAMM, 3 indicating a potential role for HA in organizing parts of the cytoplasm during phenotypic modulation. It may be also that intracellular HA provides a more compliant cytoplasmic milieu to facilitate organelle and chromosomal redistribution during cell division.
Since this article was first published, elucidating specific roles of intracellular HA has proven challenging due to the inability to perturb the intracellular compartment without disrupting extracellular HA. However, results shown here indicate that correlating a particular histochemical intracellular staining pattern with cell phenotypic events, such as cell division and migration, provide insight into key regulatory mechanisms of cell division. Many questions remain. The importance of specific ECM molecules inside cells needs further scrutiny.
