The transcription factor BCL6 is a known driver of oncogenesis in lymphoid malignancies, including diffuse large B cell lymphoma (DLBCL). Disruption of its interaction with transcriptional repressors interferes with the oncogenic effects of BCL6. We used a structure-based drug design to develop highly potent compounds that block this interaction. A subset of these inhibitors also causes rapid ubiquitylation and degradation of BCL6 in cells. These compounds display significantly stronger induction of expression of BCL6-repressed genes and anti-proliferative effects than compounds that merely inhibit co-repressor interactions. This work establishes the BTB domain as a highly druggable structure, paving the way for the use of other members of this protein family as drug targets. The magnitude of effects elicited by this class of BCL6-degrading compounds exceeds that of our equipotent non-degrading inhibitors, suggesting opportunities for the development of BCL6-based lymphoma therapeutics.

No abstract

No abstract

We have investigated the suitability of proteomics for identification of tumor-associated antigens. First, we compared the proteomes of nontumorous kidney and renal cell carcinoma (RCC) by two-dimensional gel electrophoresis (2-DE) and silver staining. Protein patterns were markedly different (approximately 800 spots in RCCs versus approximately 1400 spots in kidney). 2-DE immunoblotting revealed five RCC-specific spots, reproducibly reactive with RCC-patient but not healthy donor control sera. Two of these antigens were isolated by preparative 2-DE, and identified by Edman sequencing of tryptic peptides. The first antigen, smooth muscle protein 22-alpha (SM22-alpha), is an actin-binding protein of unknown function predominantly expressed in smooth muscle cells. In situ hybridization revealed that SM22-alpha is not expressed in the malignant cells but in mesenchymal cells of the tumor stroma. The second antigen represents carbonic anhydrase I (CAI), an isoform usually not expressed in kidney. Interestingly, a different isoform (CAXII) has previously been identified by serological expression cloning as an antigen overexpressed in some RCCs. In additional assays, antibodies to recombinant CAI or SM22-alpha were detected in sera from 3/11 or 5/11 RCC patients, respectively, whereas sera from 13 healthy individuals did not react. In conclusion, serological proteome analysis may be a new tool for the identification of tumor-associated antigens.

The ERK cascade is activated by hormones, cytokines, and growth factors that result in either proliferation or growth arrest depending on the duration and intensity of the ERK activation. Here we provide evidence that the MEK1/ERK module preferentially provides proliferative signals, whereas the MEK2/ERK module induces growth arrest at the G 1 /S boundary. Depletion of either MEK subtype by RNA interference generated a unique phenotype. The MEK1 knock down led to p21 cip1 induction and to the appearance of cells with a senescencelike phenotype. Permanent ablation of MEK1 resulted in reduced colony formation potential, indicating the importance of MEK1 for long term proliferation and survival. MEK2 deficiency, in contrast, was accompanied by a massive induction of cyclin D expression and, thus, CDK4/6 activation followed by nucleophosmin hyperphosphorylation and centrosome over-amplification. Our results suggest that the two MEK subtypes have distinct ways to contribute to a regulated ERK activity and cell cycle progression.The extracellular-regulated kinase (ERK) 1 cascade is one of three major mitogen-activated protein kinase cascades. It is predominantly involved in the control of cell proliferation, migration, cell division, and differentiation (1-3). This pathway, consisting of Raf, MEK1/2, and ERK1/2, regulates cell proliferation via its impact on cell cycle control (4). A number of observations demonstrate the importance of this cascade in the regulation of cell cycle progression. Activated variants of Raf and MEK are capable of promoting cell cycle reentry and even transformation (5-7), whereas inhibition of the ERK pathway by different means results in G 1 arrest in a variety of cell types (5,8). Activation of the ERK cascade has also been shown under certain conditions to induce cell cycle arrest (4) and even differentiation (9). Activated ERK1/2 translocates to the nucleus (10) and phosphorylates transcription factors like Ets and AP-1 family members, thereby positively regulating their activity (11). The magnitude and duration of ERK activity are, therefore, the crucial parameters determining the quality of gene expression (4).Activation of this mitogen-activated protein kinase pathway promotes the expression of cyclin D1 (12, 13) and the CDK2 inhibitory protein p21 cip1 (14). These key events result in the activation of the cyclin-dependent protein kinases CDK4/6, which promote cell cycle entry by phosphorylating the retinoblastoma tumor suppressor (Rb), leading to the release of the transcription factor E2F (15). This in turn promotes the transcription of cyclins A and E, resulting in the activation of CDK2. Activated CDK2 phosphorylates Rb at additional sites and, thus, enables DNA synthesis and centrosome duplication via further liberation of E2F (16). Furthermore, sustained expression of p21 cip1 has been shown to be responsible for the ERK-mediated proliferation inhibition (6).MEK1 and MEK2 show high homology only in their kinase domains. The N termini and the characteristic proline-rich inserts...