Cell interaction genes

The evidence to date indicates that the cell-interaction genes involved in T-B cell interactions map in the / region, more specifically in the I-A and/or I-B subregions. The location of Cl genes involved in macrophage-T cell interactions and those possibly involved in T-T interactions are not as clearly mapped as yet. 

Hie terms oncogene and tumor suppressor gene do not give any information about the actual function of the gene or the protein for which they code. Both are coupled in a complex way to different positions in the network of proliferation regulation and in cell-cell interactions, as shown in the examples below. 

A number of tumor suppressor genes are known with no direct relationship to the regulation of the cell cycle. Some of the tumor suppressor genes in Table 14.2 are involved in the organization of the cytoskeleton or in cell-cell interactions. 

Through regulation of gene transcription, cyclosporine inhibits interleukin-1 and interleukin-2 receptor production and secondarily inhibits macrophage-T-cell interaction and T-cell responsiveness (see Chapter 55). T-cell-dependent -cell function is also affected. 

FIGURE 26-31 Rous sarcoma vims genome. The src gene encodes a tyrosine-specific protein kinase, one of a class of enzymes known to function in systems that affect cell division, cell-cell interactions, and intercellular communication (Chapter 12). The same gene is found in... 

The cadherins are calcium-dependent adhesion proteins that mediate direct cell-cell interactions.295 296 The external parts of the cadherins also have repeated structural domains with the Ig fold.297 298b They have high affinity for each other, allowing cadherins from two different cells to interact and tie the cells together with a zipper-like interaction that is stabilized by the bound Ca2+ ions,297 300 and may be relatively long-lived. The gene for cadherin E is often mutated in breast cancers and may be an important tumor suppressor gene (Box 11-D).301... 

In eukaryotic cells, a gene consists of the transcribed portion, as well as the 5 and 3 flanking regulatory DNA sequences. Transcription initiation is usually regulated by the 5 regulatory sequences, which include some common DNA elements. One of these elements, the TATA box (TATAAA), is located 25-35 base pairs upstream of the transcription start site for RNA polymerase II, and its function is to direct the transcription at the so-called cap site (Breathnach and Chambon, 1981). The CAAT box (GGCCAATCT) is known to be present upstream of the TATA box. Transcription is initiated by an interaction between these DNA elements and regulatory proteins. 

Lyons, M.A., Brown, A.J. 2000. Oxysterols in atherogenesis. In Atherosclerosis, Gene Expression, Cell Interactions, and Oxidation (R.T. Dean, D. Kelly, eds.), pp. 348-370, Oxford University Press, Oxford. 

Phosphorylation dephosphorylation modifies protein structure and function and protein-protein interactions. The consequences are many. Phosphorylation of a protein may signal its destruction or may prevent it. It may control the activity of an enzyme or may determine its location in the cell. Phosphorylation dephosphorylation can modulate the activity of transcription factors and control gene expression, and phosphorylation dephosphorylation may regulate cell-cell interactions. 

Thymocytes produced in the bone marrow do not express the T-cellreceptor complex, CD4, or CDS. On relocation to the thymus and rearrangement of the T-cell-receptor genes, the immature thymocyte expresses all of these molecules. These cells are first subjected to positive selection (Figure 33.40). Cells for which the T-cell receptor can bind with reasonable affinity to either class I or class II MHC molecules survive this selection those for which the T-cell receptor does not participate in such an interaction undergo apoptosis and die. The affinities of interaction required to pass this selection are relatively modest, and so contacts between the T-cell receptor and the MHC molecules themselves are sufficient without any significant contribution from the bound peptides (which will be derived from proteins in the thymus). The role of the positive selection step is to prevent the production ofT cells that will not bind to any MHC complex present, regardless of the peptide bound. 

Bryant, P. J., Watson, K. L., Justice, R. W. and Woods, D. F. (1993). Tumor suppressor genes encoding proteins required for cell interactions and signal transduction in Drosophila. Dev. SuppL, 239-249. 

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