CD9

Crystal structure of human CD9

CD9 is a protein that in humans is encoded by the CD9 gene. It is a member of the Tetraspanin family, a group of cell surface proteins with four transmembrane domains. CD9 plays a significant role in cell adhesion, motility, and proliferation. It is involved in various cellular processes, including sperm-egg fusion during fertilization, and is also implicated in the progression of several diseases, such as cancer and infectious diseases.

Function

CD9 is widely expressed in various cell types and tissues. It functions primarily by mediating signal transduction events that affect cell adhesion and migration. CD9 forms complexes with other membrane proteins, including integrins, and these interactions are crucial for the modulation of cell adhesion to the extracellular matrix and for cell-cell interactions. This protein is also involved in the regulation of membrane fusion and vesicle trafficking, playing a vital role in reproductive biology by facilitating sperm-egg fusion.

In the immune system, CD9 is found on the surface of B cells, T cells, monocytes, and platelets, where it participates in the immune response by modulating cell activation and migration. Its expression on exosomes, small vesicles released by cells, suggests a role in intercellular communication.

Clinical Significance

Alterations in CD9 expression have been associated with various pathological conditions. In oncology, CD9 expression is often altered in tumor cells, and its presence or absence can influence tumor progression, metastasis, and patient prognosis. For example, reduced CD9 expression has been linked to increased tumor aggressiveness and poor prognosis in certain types of cancer, such as breast and pancreatic cancer.

In addition to its role in cancer, CD9 is also involved in the pathogenesis of infectious diseases. It can act as a receptor or co-receptor for pathogens, facilitating their entry into cells. Its role in viral infections, including HIV, has been studied, highlighting the importance of CD9 in the infectious disease process.

Research and Therapeutic Potential

Given its involvement in critical cellular processes and disease progression, CD9 has been explored as a target for therapeutic intervention. Antibodies targeting CD9 have been investigated for their potential to inhibit tumor growth and metastasis. Moreover, manipulating CD9 expression or function could offer new approaches to control infectious diseases and improve reproductive health.

See Also

• Tetraspanin
• Cell adhesion
• Cancer metastasis
• Exosome (vesicle)