Biomedical subjects

Barbara A Niemeyer

Publications and source records attributed to Barbara A Niemeyer.

6 recordsLinked to original sources

PubMed2006

Trafficking and assembly of the cold-sensitive TRPM8 channel.

TRPM (transient receptor potential melastatin-like) channels are distinct from many other members of the transient receptor potential family in regard to their overall size (>1000 amino acids), the lack of N-terminal ankyrin-like repeats, and hydrophobicity predictions that may allow for more than six transmembrane regions. Common to each TRPM member is a prominent C-terminal coiled coil region. Here we have shown that TRPM8 channels assemble as multimers using the putative coiled coil region within the intracellular C terminus and that this assembly can be disturbed by a single point mutation within the coiled coil region. This mutant neither gives rise to functional channels nor do its subunits interact or form protein complexes that correspond to a multimer. However, they are still transported to the plasma membrane. Furthermore, wild-type currents can be suppressed by expressing the membrane-attached C-terminal region of TRPM8. To separate assembly from trafficking, we investigated the maturation of TRPM8 protein by identifying and mutating the relevant N-linked glycosylation site and showing that glycosylation is neither essential for multimerization nor for transport to the plasma membrane per se but appears to facilitate efficient multimerization and transport.

Animals↗

PubMed2005

TRPV6 potentiates calcium-dependent cell proliferation.

The Ca(2+) homeostasis within cells controls a diversity of cellular processes including gene transcription, proliferation and apoptosis. Perturbance of Ca(2+) signaling may induce deregulation of cell proliferation and suppression of cell death providing the basis for cancer development. In human prostate cancer, a correlation between the mRNA expression of the Ca(2+) channel TRPV6 and the staging of the cancer has been described. We have analyzed the influence of TRPV6 on cell proliferation within HEK-293 cells. We show that TRPV6 increases cell proliferation of HEK-293 cells in a Ca(2+) dependent manner. The increased proliferation correlates with slightly increased intracellular Ca(2+) levels without interfering with the intrinsic Ca(2+) dependence of HEK-293 cell proliferation. Low doses of econazole inhibit both, TRPV6 dependent Ca(2+) signals and cell proliferation while BTP2, a potent inhibitor of Ca(2+) signals and cell proliferation in T-cells, neither influences TRPV6 dependent Ca(2+) signals nor cell proliferation of HEK-293 cells. Our data demonstrate that TRPV6 increases the rate of Ca(2+) dependent cell proliferation which is a prerequisite for its potential role in tumor progression.

Anilides↗

PubMed2005

Structure-function analysis of TRPV channels.

In recent years many new members of the family of TRP ion channels have been identified. These channels are classified into several subgroups and participate in many sensory and physiological functions. TRPV channels are important for the perception of pain, temperature sensing, osmotic regulation, and maintenance of calcium homeostasis, and much recent research concerns the identification of protein domains involved in mediating specific channel functions. Recent literature on TRPV channel subunit composition, protein domains required for subunit assembly, trafficking, and regulation will be reviewed and discussed.

Animals↗

PubMed2004

Ca2+-selective transient receptor potential V channel architecture and function require a specific ankyrin repeat.

Transient receptor potential (TRP) proteins form cation-conducting ion channels with currently 28 known genes encoding TRP channel monomers in mammals. These monomers are thought to coassemble to form homo- or heterotetrameric channels, but the signals governing their assembly are unknown. Within the TRPV subgroup, TRPV5 and TRPV6 show exclusive calcium selectivity and play an important role in calcium uptake. To identify signals that mediate assembly of functional TRPV6, we screened domains for self-association using co-immunoprecipitation, sucrose gradient centrifugation, bacterial two-hybrid assays, and patch clamp analysis. Of the two identified interaction domains within the N-terminal region, we showed that the first domain encompassing the third ankyrin repeat is the stringent requirement for physical assembly of TRPV6 subunits and when transferred to an unrelated protein enables its interaction with TRPV6. Deletion of this repeat or mutation of critical residues within this repeat rendered nonfunctional channels that do not co-immunoprecipitate or form tetramers. Suppression of dominant-negative inhibitors of TRPV6-specific currents was achieved by deletion of ankyrin (ANK) 3. We propose that the third ANK repeat initiates a molecular zippering process that proceeds past the fifth ANK repeat and creates an intracellular anchor that is necessary for functional subunit assembly.

Amino Acid Sequence↗

PubMed2004

TRP channels as potential drug targets.

Calcium (Ca2+) is an ubiquitous intracellular signal that is responsible for a plethora of cellular processes including fertilization, secretion, contraction, neuronal signaling and learning. In addition, changes in intracellular Ca2+ have been known to influence cell proliferation and differentiation for more than three decades. Recent studies have indicated that members of the transient receptor potential (TRP) family of ion channels which respond to many different modes of stimulation both from within and outside the cell may be a primary mode of cation and Ca2+ entry into cells and may have roles in growth control. Moreover, changes in the expression of these channels may contribute to certain cancers. In the following, recent results concerning the expression and function of members of this family of ion channels are summarized.

Animals↗

PubMed2002

Members of the synaptobrevin/vesicle-associated membrane protein (VAMP) family in Drosophila are functionally interchangeable in vivo for neurotransmitter release and cell viability.

Synaptobrevins or VAMPs are vesicle-associated membrane proteins, often called v-SNARES, that are important for vesicle transport and fusion at the plasma membrane. Drosophila has two characterized members of this gene family: synaptobrevin (syb) and neuronal synaptobrevin (n-syb). Mutant phenotypes and gene-expression patterns indicate that n-Syb is exclusively neuronal and required only for synaptic vesicle secretion, whereas Syb is ubiquitous and, as shown here, essential for cell viability. When the eye precursor cells were made homozygous for syb(-), the eye failed to develop. In contrast, n-syb(-) eye clones developed appropriately but failed to activate downstream neurons. To determine whether the two proteins are structurally specialized to accomplish these distinct in vivo functions, we have driven the expression of each gene in the absence of the other to look for phenotypic rescue. We find that expression of n-syb during eye development can rescue the cell lethality of the syb mutations, as can rat VAMP2 and cellubrevin. Expression of syb can restore synaptic transmission to n-syb mutants as assayed both by electroretinogram and recordings of excitatory junctional currents at the neuromuscular junction. Therefore, we find that Syb, which usually is not involved in synaptic function, can mediate Ca(2+)-triggered synaptic activity and that no particular specialization of the v-SNARE is required to differentiate synaptic exocytosis from other forms.

Animals↗