Role of PKCepsilon-modulated genes

Protein kinase C is a family of 10 related proteins (denominated alpha, betaI, betaII, gamma, delta, eta, epsilon, theta, iota und zeta). These proteins seem to play a role in different diseases such as allergy, asthma, rheumatoid arthritis, AIDS, Alzheimers disease, multiple sclerosis, hypertension, cardiac hypertrophy, atherosclerosis, diabetes and cancer. LY333531 (Ruboxistaurin) is an inhibitor of protein kinase C betaI and II. In clinical tests the compound showed, that it can prevent diabetic complications (diabetic foot is a combination of blood vessel and neurologic damage, diabetic polyneuropathy is a damage of neurons, diabetic retinopathy is a disease of small blood vessels in the eye, diabetic nephropathy is damage of the kidneys). The exact function of the 10 protein kinase C proteins is not known at present. We want to elucidate the function of protein kinase C epsilon. It might be involved in carcinogenesis, cardiac failure, alcohol consumption and pain sensitivity. Knowledge of the exact function of protein kinase C epsilon would be important for the development of potential new drugs in these areas. We found previously that protein kinase C epsilon increases the expression of one gene and down-modulates 30 others. The major part of these genes were unknown so far. We have investigated two down-modulated, unknown genes and the proteins produced by them (they are denominated C6orf69 and RHOBTB3). From both genes only parts were known. We elucidated the full length genes and proteins. Both proteins contain a BTB/POZ domain which seems to be involved in the regulation of genes or binding to other proteins. This suggests, that these proteins are involved in regulation mechanisms in the cell. In our investigations performed so far we obtained indications that C6orf69 seems to interact with other proteins and might be able to regulate their degradation. In the proposed project we to investigate with which proteins both of the investigated proteins interact and whether they regulate their degradation. We expect to obtain new information about regulations in cells. This information could also lead to new cognitions about the function of protein kinase C epsilon. A long-term goal is to find out whether inhibitors of the activities of C6orf69 or RHOBTB3 could be used for treatment of cancer or other diseases mentioned above.

Protein kinase C epsilon (PKCepsilon) is a protein which seems to play a role in tumor metastasis, diabetes, cardiac insufficiency, pain or alcoholism. In order to obtain additional information, we investigated the influence of PKCepsilonon the expression of other genes. We found that PKCepsilon upregulates a part of another gene. We could identify the full- length gene. It turned out to be the excision repair cross-complementing rodent repair deficiency complementation group 6like gene (ERCC6L) gene. A series of other genes was down-modulated by PKCepsilon. From most of these genes only a part of the sequence was known. From two of these genes we identified the full-length genes. These genes turned out to be chromosome 6 open reading frame 69 (C6orf69) and Rho-related BTB domain- containing protein 3 (RhoBTB3). Both proteins contain a BTB/POZ domain which is usually involved in protein-protein interactions. Therefore, we were interested in proteins interacting with C6orf69 or RhoBTB3. We found that RhoBTB3 binds to Cullin 3. Starting with C6orf69, we found the following interactions: A B C D E F PKC C6orf69 C6orf69 C6orf69 C6orf69BTBD10 C6orf69C6orf69 Cul3 ActinBTBD10Akt One result of our investigations was that C6orf69 interacts with BTBD10. This protein contains, as well as C6orf69 and RhoBTB3, a BTB/POZ domain. Since both, RhoBTB3 and C6orf69, are ubiquinated (attachement of an ubiquitin protein) and bind to Cullin 3, they might play a potential role in the degradation of certain proteins. The exact functions of C6orf69, RhoBTB3 and BTBD10 as well as that of the protein-protein interactions shown above has to be found out in further investigations. An important result from this project is that C6or69 exhibited higher expression in 7 out of 8 human breast tumor cell lines compared with non-tumorigenic breast epithelial cells. 9 out of 9 breast tumors showed higher expression of C6orf69 compared with matched normal adjacent breast tissue from the same patient. An elevated expression of C6orf69 in comparison with normal tissue could be detected only in breast tumors but not in other tumors. Therefore, C6orf69 might play a role in breast tumors and might be a target for the treatment of breast cancers.