CEBPA

Function

The protein encoded by this intronless gene is a bZIP transcription factor which can bind as a homodimer to certain promoters and enhancers. It can also form heterodimers with the related proteins CEBP-beta and CEBP-gamma, as well as distinct transcription factors such as Jun. The encoded protein has been shown to bind to the promoter and modulate the expression of the gene encoding leptin, a protein that plays an important role in body weight homeostasis. Also, the encoded protein can interact with CDK2 and CDK4, thereby inhibiting these kinases and causing growth arrest in cultured cells.. In addition, CEBPA is essential for myeloid lineage commitment and therefore required both for normal mature granulocyte formation and for the development of abnormal AML .

Common mutations

There are two major categories which CEBPA mutations can be categorized into. One category of mutations prevent CCAAT/enhancer-binding protein alpha DNA binding by altering its COOH-terminal basic leucine zipper domain. The other category of mutations disrupt the translation of the CCAAT/enhancer-binding protein alpha NH₂ terminus. CEBPA mutations, which result in diminished CCATT/enhancer-binding protein alpha activity, contribute to the transformation of myeloid antecedents.

Interactions

CEBPA has been shown to interact with Cyclin-dependent kinase 2 and Cyclin-dependent kinase 4.

Clinical significance

It has been shown that mutation of CEBPA has been linked to good outcome in both adult and pediatric acute myeloid leukemia patients.

Significance in acute myeloid leukemia

Acute myeloid leukemia is characterized by genetic abnormalities in hematopoietic progenitors. This includes excessive proliferation of blasts, and blocking the hematopoiesis of ganulocytes. It has been shown that suppression of CEBPA expression and blocking of CCAAT/enhancer-binding protein alpha stops the differentiation of myeloid progenitors. For this reason, CCAAT/enhancer-binding protein alpha's role during granulocyte differentiation and CEBPA's role as a tumor suppressor gene is critically important in the prognosis of acute myeloid leukemia.

Prognostic significance of CEBPA mutations

CCAAT/enhancer-binding protein alpha, the transcription factor that is encoded by CEBPA, is very important in the differentiation of immature granulocytes. Mutation of the CEBPA gene has been shown to play a crucial role in leukemogenesis and prognosis in acute myeloid leukemia patients. In recent studies CEBPA mutations were found in between 7% and 15% of patients with acute myeloid leukemia. The three different types of mutations seen in these AML patients include germ-line N-terminal mutation, N-terminal frameshift mutation, and C-terminal mutation. These mutations are most frequently found in acute myeloid leukemia M1 or acute myeloid leukemia M2. Many reports link CEBPA mutations with a favorable outcome in acute myeloid leukemia. This is because these mutations are liley to induce differentiation arrest in these patients. Patients with CEBPA mutations have longer remission duration and survival time than those without the mutations. Therefore the presence of CEBPA mutations are directly associated with a more favorable course for the progression of the disease.

Significance in solid tumors

Recently it has been shown that epigenetic modification of the distal promoter region of CEBPA has resulted in downregulation of CEBPA expression in pancreatic cancer cells, lung cancer, and head and neck squamous cell carcinoma.

Methylation of CEBPA as a prognostic biomarker in AML patients

A recent study has found that higher levels of CEBPA methylation are directly proportionate with treatment response. The complete response rate increased proportionately with the level of CEBPA methylation. For this reason it has been proposed that methylation of CEBPA could be a very useful biomarker in acute myeloid leukemia prognosis.