CBP (HMV319)

CBP (CREB-binding protein) is a histone acetyltransferase coded by the CREBBP gene on chromosome 16p13.3.  CBP co-operates closely with p300, another histone acetyltransferase with functional overlap and considerable sequence homology. Both p300 and CBP interact with numerous transcription factors to increase the expression of their target genes. They are thought to relax the chromatin structure at gene promoters through their intrinsic histone acetyltransferase activity, to recruit the basal transcriptional machinery including RNA polymerase II to the promoter, and to act as adaptor molecules. CBP and p300 are critical for normal embryonic development, as mice completely lacking either CBP or p300 protein, die at an early embryonic stage. That mice with a lack of one functional copy of both the CBP and p300 genes and thus having half of the normal amount of both CBP and p300 also die early in embryogenesis suggests that the total amount of CBP and p300 protein is critical for embryo development. Some cell types may tolerate a loss of CBP or p300 better than the whole organism can. Mutations in CBP (and more rarely p300) are the cause of the Rubinstein-Taybi Syndrome which is characterized by severe mental retardation. As these mutations are typically leading to the production of a very short, nonfunctional version of the CBP or p300 protein or prevent one copy of the gene from making any protein at all, it becomes clear that the loss of one copy of the CBP or p300 gene severely disrupts normal development. CBP has been shown to play a role in the etiologies of several other diseases including diabetes, schizophrenia, Alzheimer’s disease, depression, other neurological conditions, hematologic malignancies, and solid tumors. CBP has been shown to play a role in every stage of cancer development. Although mice which are heterozygous for CBP (Cbp+/-) showed an increased incidence of leukemia or hematologic neoplasia, CBP is generally considered an oncogene due to its critical role in regulation of cell proliferation, growth, migration and apoptosis. CBP overexpression has been linked to tumorigenesis, metastasis, immune evasion and drug-resistance. Given the pivotal role of CBP for a wide variety of physiological processes, numerous CBP inhibitors have been developed, some of which have progressed into clinical trials.

Images describing the CBP staining pattern in normal tissues obtained by the antibody HMV319 are shown in our “Normal Tissue Gallery”.

These findings are largely consistent with the RNA data described in the Human Protein Atlas (Tissue expression CBP). 

Positive control = Testis: A strong nuclear CBP staining should be seen in Sertoli and Leydig cells as well as in spermatogonia.

Negative control = Testis: The nuclear CBP staining intensity decreases during the maturation of spermatocytes while spermatids are completely CBP negative.

Normal tissue gallery

Cancer tissue gallery

No data available at the moment

IHC users have different preferences on how the stains should look like. Some prefer high staining intensity of the target stain and even accept some background. Others favor absolute specificity and lighter target stains. Factors that invariably lead to more intense staining include higher concentration of the antibody and visualization tools, longer incubation time, higher temperature during incubation, higher temperature and longer duration of the heat induced epitope retrieval (slide pretreatment). The impact of the pH during slide pretreatment has variable effects and depends on the antibody and the target protein.

All images and data shown here and in our image galleries are obtained by the manual protocol described below. Other protocols resulting in equivalent staining are described as well.

Manual protocol

Freshly cut sections should be used (less than 10 days between cutting and staining). Heat-induced antigen retrieval for 5 minutes in an autoclave at 121°C in pH 7,8 Target Retrieval Solution buffer. Apply HMV319 at a dilution of 1:150 at 37°C for 60 minutes. Visualization of bound antibody by the EnVision Kit (Dako, Agilent) according to the manufacturer’s directions.

• The role of CBP as a therapeutic target needs to be further investigated.
• The predictive and prognostic role of CBP immunohistochemistry should be investigated.
• The role CBP in metabolic and neurologic disorders needs to be further evaluated.

There are two ways how the specificity of antibodies can be documented for immunohistochemistry on formalin fixed tissues. These are: 1. Comparison with a second independent method for target expression measurement across a large number of different tissue types (orthogonal strategy), and 2. Comparison with one or several independent antibodies for the same target and showing that all positive staining results are also seen with other antibodies for the same target (independent antibody strategy). 

Orthogonal validation: For the antibody HMV319 specificity is supported by the good concordance of the immunostaining data with data from three independent RNA screening studies, including the Human Protein Atlas (HPA) RNA-seq tissue dataset, the FANTOM5 project, and the Genotype-Tissue Expression (GTEx) project, which are all summarized in the Human Protein Atlas (Tissue expression CBP). In agreement with HMV319 immunostaining data, CBP RNA expression predominated in the bone marrow and lymphoid tissues, and was also seen in other organs. However, orthogonal validation is not optimal for assessing ubiquitously expressed proteins.

Comparison of antibodies: True expression of CBP in all cell types with CBP positivity by HMV319 is corroborated by an identical staining obtained by a commercially available independent second antibody (termed “validation antibody”). Most of all, both antibodies showed identical tissue specific heterogeneity of staining such as absence of CBP staining in trophoblastic cells of the mature (but not the early) placenta, and a continuous decrease of CBP staining intensity along the maturation of spermatocytes (spermatids are completely CBP negative).

Normal tissue gallery