Biomedical subjects

Deborah A Lannigan

Publications and source records attributed to Deborah A Lannigan.

7 recordsLinked to original sources

PubMed2006

Homology model of RSK2 N-terminal kinase domain, structure-based identification of novel RSK2 inhibitors, and preliminary common pharmacophore.

Ribosomal S6 kinase 2 (RSK2) is a serine/threonine kinase that plays a role in human cancer and Coffin-Lowry syndrome and is comprised of two nonidentical kinase domains, each domain with its own ATP-binding site. RSK2 can be inactivated by different types of small organic molecules. Potent RSK2 inhibitors include the two classic bisindole maleimide PKC inhibitors, Ro31-8220 and GF109203X, and the natural product SL0101 that was shown to bind specifically to the ATP pocket of the N-terminal domain (NTD). In this paper, we present an atomic model of the RSK2 NTD (residues 68-323), which was built to simultaneously bind the distinctive molecular scaffolds of SL0101, Ro31-8220, and GF109203X. The RSK2 NTD model was used to identify two novel RSK2 inhibitors from the National Cancer Institute open chemical repository and to develop a preliminary structure-based pharmacophore model.

Benzopyrans↗

PubMed2006

Influence of rhamnose substituents on the potency of SL0101, an inhibitor of the Ser/Thr kinase, RSK.

We have previously reported the isolation of kaempferol 3-O-(3'',4''-di-O-acetyl-alpha-l-rhamnopyranoside) from Forsteronia refracta [Xu, Y.-M.; Smith, J. A.; Lannigan, D. A.; Hecht, S. M. Biorg. Med. Chem.2006, 14, 3974-3977.]. This flavonoid glycoside, termed SL0101, is a specific inhibitor of p90 ribosomal S6 kinase (RSK) with a dissociation constant of 1 microM. In intact cells, however, the EC50 for inhibition of RSK activity is 50 microM, which suggests that the efficacy of SL0101 could be limited by cellular uptake. Therefore, we investigated the possibility of developing a more potent RSK inhibitor by synthesizing SL0101 analogs with increased hydrophobic character. The total syntheses of kaempferol 3-O-(3'',4''-di-O-butyryl-alpha-L-rhamnopyranoside) (Bu-SL0101) and kaempferol 3-O-(2'',3'',4''-tri-O-acetyl-alpha-L-rhamnopyranoside) (3Ac-SL0101) were performed. The IC50 for inhibition of RSK activity in in vitro kinase assays for the analogs was similar to that obtained for SL0101. 3Ac-SL0101 demonstrated the same remarkable specificity for inhibiting RSK activity in intact cells as SL0101; however, Bu-SL0101 was not completely specific. 3Ac-SL0101 was approximately 2-fold more potent at inhibiting MCF-7 cell proliferation compared to SL0101 and preferentially decreased MCF-7 cell growth, as compared to the growth of the normal human breast line, MCF-10A. Thus the discovery of 3Ac-SL0101 as a more potent RSK-specific inhibitor than SL0101 should facilitate the development of RSK inhibitors as anti-cancer chemotherapeutic agents.

Antineoplastic Agents↗

PubMed2006

Three acetylated flavonol glycosides from Forsteronia refracta that specifically inhibit p90 RSK.

A survey of plant extracts for the presence of p90 ribosomal S6 kinase (RSK) inhibitors resulted in the isolation of three acetylated flavonol glycosides. Kaempferol 3-O-(2'',4''-O-diacetyl-alpha-l-rhamnopyranoside) (1), kaempferol 3-O-(3'',4''-O-diacetyl-alpha-l-rhamnopyranoside) (2), and kaempferol-3-O-(4''-O-acetyl-alpha-l-rhamnopyranoside) (3) were isolated from Forsteronia refracta as the first RSK inhibitors. Of these, compound 2 was found to be the best inhibitor with an IC(50) value of 89 nM.

Acetylation↗

PubMed2005

Identification of the first specific inhibitor of p90 ribosomal S6 kinase (RSK) reveals an unexpected role for RSK in cancer cell proliferation.

p90 ribosomal S6 kinase (RSK) is an important downstream effector of mitogen-activated protein kinase, but its biological functions are not well understood. We have now identified the first small-molecule, RSK-specific inhibitor, which we isolated from the tropical plant Forsteronia refracta. We have named this novel inhibitor SL0101. SL0101 shows remarkable specificity for RSK. The major determinant of SL0101-binding specificity is the unique ATP-interacting sequence in the amino-terminal kinase domain of RSK. SL0101 inhibits proliferation of the human breast cancer cell line MCF-7, producing a cell cycle block in G(1) phase with an efficacy paralleling its ability to inhibit RSK in intact cells. RNA interference of RSK expression confirmed that RSK regulates MCF-7 proliferation. Interestingly, SL0101 does not alter proliferation of a normal human breast cell line MCF-10A, although SL0101 inhibits RSK in these cells. We show that RSK is overexpressed in approximately 50% of human breast cancer tissue samples, suggesting that regulation of RSK has been compromised. Thus, we show that RSK has an unexpected role in proliferation of transformed cells and may be a useful new target for chemotherapeutic agents. SL0101 will provide a powerful new tool to dissect the molecular functions of RSK in cancer cells.

Amino Acid Sequence↗

PubMed2005

Novel biosensors for the detection of estrogen receptor ligands.

There exists a significant need for the detection of novel estrogen receptor (ER) ligands for pharmaceutical uses, especially for treating complications associated with menopause. We have developed fluorescence resonance energy transfer (FRET)-based biosensors that permit the direct in vitro detection of ER ligands. These biosensors contain an ER ligand-binding domain (LBD) flanked by the FRET donor fluorophore, cyan fluorescent protein (CFP), and the acceptor fluorophore, yellow fluorescent protein (YFP). The ER-LBD has been modified so that Ala 430 has been changed to Asp, which increases the magnitude of the FRET signal in response to ligand-binding by more than four-fold compared to the wild-type LBD. The binding of agonists can be distinguished from that of antagonists on the basis of the distinct ligand-induced conformations in the ER-LBD. The approach to binding equilibrium occurs within 30min, and the FRET signal is stable over 24h. The biosensor demonstrates a high signal-to-noise, with a Z' value (a statistical determinant of assay quality) of 0.72. The affinity of the ER for different ligands can be determined using a modified version of the biosensor in which a truncated YFP and an enhanced CFP are used. Thus, we have developed platforms for high-throughput screens for the identification of novel estrogen receptor ligands. Moreover, we have demonstrated that this FRET technology can be applied to other nuclear receptors, such as the androgen receptor.

Androgens↗

PubMed2003

Estrogen receptor phosphorylation.

Estrogen receptor alpha (ERalpha) is phosphorylated on multiple amino acid residues. For example, in response to estradiol binding, human ERalpha is predominately phosphorylated on Ser-118 and to a lesser extent on Ser-104 and Ser-106. In response to activation of the mitogen-activated protein kinase pathway, phosphorylation occurs on Ser-118 and Ser-167. These serine residues are all located within the activation function 1 region of the N-terminal domain of ERalpha. In contrast, activation of protein kinase A increases the phosphorylation of Ser-236, which is located in the DNA-binding domain. The in vivo phosphorylation status of Tyr-537, located in the ligand-binding domain, remains controversial. In this review, I present evidence that these phosphorylations occur, and identify the kinases thought to be responsible. Additionally, the functional importance of ERalpha phosphorylation is discussed.

Cyclic AMP-Dependent Protein Kinases↗

PubMed2003

Extracellular signal-regulated kinase 7, a regulator of hormone-dependent estrogen receptor destruction.

Estrogen receptor alpha (ER alpha) degradation is regulated by ubiquitination, but the signaling pathways that modulate ER alpha turnover are unknown. We found that extracellular signal-regulated kinase 7 (ERK7) preferentially enhances the destruction of ER alpha but not the related androgen receptor. Loss of ERK7 was correlated with breast cancer progression, and all ER alpha-positive breast tumors had decreased ERK7 expression compared to that found in normal breast tissue. In human breast cells, a dominant-negative ERK7 mutant decreased the rate of endogenous ER alpha degradation >4-fold in the presence of hormone and potentiated estrogen responsiveness. ERK7 targets the ER alpha ligand-binding domain for destruction by enhancing its ubiquitination. Thus, ERK7 is a novel regulator of estrogen responsiveness through its control of ER alpha turnover.

Animals↗