Growth Factors and Cytokines Review

By: Jennifer Fries, BioFiles 2009, 4.5, 3.

 

Jennifer Fries
Technical Marketing Specialist, Cell Culture

Introduction

The importance of cytokines and growth factors in cell culture has been demonstrated time and time again since the inception of cell culture. Beginning with the first successful efforts of growing cells in culture, there have been so called ‘secret ingredients’ added to culture medium that have, over time, given rise to a the belief that cell culture is as much of an art as a technique. Serum and other < extracts and the painstaking, continued attempts to characterize them have greatly contributed to this situation.

Studies published as early as 1921 acknowledged the fact that there were critical unknowns that were essential for normal growth, metabolism, and development of cells in culture. Zilva, Goldblatt, Sanford and a number of other cell biology pioneers were the first to admit that there were unknown factors influencing the general health of both cellular and animal models.

Over time, we have learned that many of these unknown factors are nutrients such as vitamins, amino acids, sugars, albumins and transferrins. However, even when all the necessary nutrients are present certain cells especially primary cells do not proliferate. Serum seemed to provide the unknown factors that encouraged cell proliferation. Today we know the agents that are responsible for cell proliferation and differentiation are growth factors and cytokines.

Growth factors can be described as proteins that bind to receptors on the cell surface of non-hematopoietic cells and result in proliferation or differentiation of the affected cells. Each family of growth factors affect specific cell types. For example, epidermal growth factors (EGF), affect epithelial cell types, similarly platelet derived growth factors(PDGF), affect only fibroblasts commonly found in connective tissues.

Cytokines, often compared with growth factors, are a class of signaling molecules (proteins, peptides and glycoproteins) that affect primarily the cells of the immune system but can affect other diverse cell types outside of the immune system as well. Cytokines are generally thought of as part of the signaling mechanism that orchestrates the immune response to bacterial infection. The effects of cytokines on cells are varied, some like growth factors cause cell proliferation, others may cause chemotaxis between different cell types, and others can even cause apoptosis.

Cytokines and growth factors are somewhat similar in their structure and mechanism of action. Both bind to specific cell surface receptors that initiate signaling pathways and well as having receptors that share distinct structural homologies. Many growth factors and cytokines also share several intracellular signaling components through which the activated cell surface receptor transmits its message to the cell nucleus.

In both the research and pharmaceutical community, there is a growing need for defined serum-free media that eliminates the variability and the potential virus and prion contamination as well as facilitates the purification of recombinant proteins. The development of serum-free media will often necessitate the use of certain growth factors, and cytokines. This is always true for primary cell lines but often necessary for transformed cell lines and hybridomas as well.

Selecting the appropriate growth factors and cytokines for your application is an important task and can be often based on existing protocols or by chance. Growth factors and cytokines are critical to successful cell differentiation and proliferation. Within this issue of BioFiles, you will find Sigma®’s listing of cell culture tested cytokines and growth factors along with helpful information that will make choosing the products you need easier.

Sigma-Aldrich® carries an extensive line of high quality, cell culture tested growth factors and cytokines to complement your research needs. Please visit us at sigma-aldrich.com/growthfactors to view our complete list on-line.

Unless otherwise stated, our cytokines and growth factors are intended for research use only.

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