Recombinant Human Prolactin receptor (PRLR)

What is the basic structure of human Prolactin Receptor?

Human Prolactin Receptor is a cytokine hematopoietic receptor protein with an extracellular domain (ECD) that binds to prolactin molecules. The receptor's extracellular domain spans from Gln25 to Asp234 in its amino acid sequence, as identified by its accession number P16471 . The functional receptor consists of a single-pass transmembrane protein that typically forms dimers upon prolactin binding. The extracellular domain contains recognition motifs that are critical for ligand-receptor interactions, while the intracellular domain mediates downstream signaling through various pathways .

How does Prolactin interact with its receptor at the molecular level?

The prolactin molecule is thought to bind to two receptor molecules, forming a signaling complex . This interaction follows a sequential binding model where one prolactin molecule first binds to one receptor molecule with high affinity, followed by recruitment of a second receptor molecule with lower affinity. The binding occurs primarily through the extracellular domain of the receptor, which contains specific binding sites that recognize distinct epitopes on the prolactin molecule. This binding initiates conformational changes that activate intracellular signaling cascades .

What are the key amino acid sequences involved in PRLR-PRL binding?

The key sequence for recombinant human PRLR typically spans from amino acids Leu29 to Cys227, which constitutes the functionally active region of the protein . In particular, the extracellular domain (ECD) of PRLR, which spans from Gln25 to Asp234, contains the critical binding sites for prolactin . Research shows that specific amino acid residues within this region are essential for the receptor-ligand interaction. The sequence is highly conserved across species, indicating its functional importance in prolactin signaling .

What expression systems are commonly used for recombinant PRLR production?

Common expression systems for recombinant PRLR production include E. coli and mammalian cell lines such as HEK293 cells. The E. coli system is typically used for producing the extracellular domain of PRLR, as demonstrated in the production of recombinant Human Prolactin/PRL protein where the target gene encoding Leu29-Cys227 is expressed . For full-length or more complex forms of PRLR requiring post-translational modifications, HEK293 cells are often preferred, as they can produce proteins with >98% purity and appropriately folded structures .

How can researchers achieve large-scale production of PRLR-ECD?

Novel protocols have been developed for large-scale preparation of human PRLR extracellular domain (PRLR-ECD). These protocols typically involve optimized expression vectors, carefully selected host systems, and refined purification strategies. The process includes gene cloning into appropriate expression vectors, transformation into host cells (such as E. coli or HEK293), induction of protein expression, cell lysis, and multiple chromatography steps for purification . These methods have demonstrated significant improvements in yield, with some protocols showing >6-fold increases in production efficiency compared to previous methods .

What are the critical quality control parameters for recombinant PRLR production?

Critical quality control parameters for recombinant PRLR production include purity, endotoxin levels, and functional activity. Purity is typically assessed using reducing SDS-PAGE, with high-quality preparations showing >95% purity . Endotoxin levels should be maintained below 1.0 EU per μg as determined by the LAL method to ensure the product is suitable for in vitro and in vivo research applications . Functional activity is assessed through binding assays with prolactin, and through biological assays measuring downstream signaling or proliferative responses in appropriate cell lines .

How can PRLR-ECD be used in binding assays to study prolactin-receptor interactions?

PRLR-ECD can be used in several types of binding assays to study prolactin-receptor interactions. One approach is a competitive non-radioactive binding assay using biotinylated human prolactin (hPRL) as the ligand and human PRLR-ECD as the receptor . Another method involves assessing the formation of stable 1:1 complexes between PRLR-ECD and prolactin (or prolactin antagonists) under non-denaturing conditions using size-exclusion chromatography . Surface plasmon resonance (SPR) methodology can also be employed to determine binding kinetics and affinity constants between PRLR-ECD and various ligands, providing real-time interaction data .

What cell-based assays can be used to evaluate PRLR signaling and functionality?

Several cell-based assays can be used to evaluate PRLR signaling and functionality. A commonly used approach is the proliferation assay using cell lines that express PRLR, such as Baf/LP cells stably expressing human PRLR or Nb2-11 rat lymphoma cells . In these assays, cell proliferation induced by prolactin can be measured, and the inhibitory effects of antagonists can be quantified. Additionally, metabolic activity assays following incubation with prolactin (PRL), PRL-antibodies, or PRLR-antibodies can be performed in various cell lines, including cancer cell lines (HeLa, SiHa, C-33A) and control cells (MCF-7, T-47D, HaCaT) .

How can researchers detect and quantify PRLR expression in different cell types?

PRLR expression in different cell types can be detected and quantified using multiple complementary techniques. Western blotting using specific antibodies against PRLR can identify the receptor proteins by their characteristic molecular weight . Immunocytochemistry can be employed to visualize the cellular localization of PRLR using secondary antibodies conjugated with fluorescent markers (such as Alexa Fluor 488) . For quantitative assessment, real-time RT-PCR can measure relative expression levels of PRLR mRNA . Additionally, flow cytometry using specific antibodies can be used to quantify cell surface expression of PRLR across different cell populations.

What is del 1-9-G129R hPRL and how does it function as a PRLR antagonist?

Del 1-9-G129R hPRL is a genetically engineered variant of human prolactin that functions as a pure antagonist of human PRL in binding to the PRLR extracellular domain. This molecule has been designed by deleting the first 9 amino acids and introducing a glycine to arginine substitution at position 129 of the human prolactin sequence . This modified protein can bind to PRLR with affinity similar to wild-type prolactin but fails to activate downstream signaling pathways. Functionally, del 1-9-G129R hPRL inhibits prolactin-induced proliferation of cells expressing PRLR, such as Baf/LP cells, making it a valuable tool for studying prolactin-dependent signaling and potential therapeutic applications .

How can researchers evaluate the efficacy of PRLR antagonists in experimental settings?

Researchers can evaluate the efficacy of PRLR antagonists through multiple complementary approaches. Competitive binding assays can assess the antagonist's ability to displace prolactin from binding to PRLR-ECD . Cell proliferation assays using cell lines like Baf/LP or Nb2-11 can measure the antagonist's capacity to inhibit prolactin-induced proliferation . Formation of stable complexes between the antagonist and PRLR-ECD can be analyzed using size-exclusion chromatography under non-denaturing conditions . Additionally, surface plasmon resonance can determine binding kinetics and affinity constants. For in vivo efficacy, the antagonist's ability to block prolactin-dependent physiological responses in appropriate animal models can be assessed .

What strategies are being developed to create high-affinity PRLR antagonists?

Novel strategies for developing high-affinity PRLR antagonists include yeast surface display methodology. In this approach, del 1-9-G129R hPRL is expressed on the surface of yeast cells where it retains its binding capacity for PRLR-ECD . This display system allows for the development of randomly mutated libraries of the del 1-9-G129R hPRL open reading frame, from which high-affinity variants can be selected through successive rounds of binding and enrichment . Another approach involves the creation of pegylated analogues of prolactin antagonists to provide long-lasting activity for in vivo experiments, although this modification may affect the biological activity in vitro .

What role does PRLR play in cancer development and progression?

PRLR plays significant roles in the development and progression of various cancers, particularly breast and prostate cancers . In cervical cancer cell lines (HeLa, SiHa, C-33A), PRLR expression has been detected at both protein and mRNA levels, with different cell lines showing variable expression patterns . Studies have demonstrated that prolactin can affect the metabolic activity and proliferation of these cancer cells, effects that can be blocked using specific PRLR antibodies . This suggests that PRLR signaling contributes to cancer cell growth and survival. The receptor's expression in various cancer types makes it a potential target for therapeutic interventions aimed at blocking prolactin-dependent tumor growth .

How do PRLR blocking antibodies affect cancer cell proliferation?

PRLR blocking antibodies can significantly impact cancer cell proliferation in a cell type-dependent manner. In cervical cancer cell lines (HeLa, SiHa, C-33A), anti-PRLR antibodies (at concentrations of 2.5 μg) can inhibit the proliferative effects of prolactin (200 ng/ml) after 3 or 5 days of treatment . Similar effects have been observed in breast cancer cell lines like MCF-7 and T-47D, which are known to express high levels of PRLR . The inhibitory effect occurs through preventing prolactin binding to its receptor, thereby blocking downstream signaling pathways that promote cell growth and survival. These findings highlight the potential therapeutic value of PRLR-targeting strategies in cancers where prolactin signaling contributes to disease progression .

How can pegylation be used to modify recombinant PRLR for enhanced in vivo applications?

Pegylation of recombinant PRLR and related proteins can create long-lasting analogues needed for in vivo experiments. This process involves the covalent attachment of polyethylene glycol (PEG) molecules to specific sites on the protein . Mono-pegylated analogues of human prolactin have been developed for this purpose, though research indicates that pegylation typically lowers biological activity in homologous in vitro assays . The primary advantage of pegylation is the significant increase in the protein's half-life in circulation, making it more suitable for in vivo studies. The optimal pegylation strategy must balance the trade-off between extended half-life and maintained biological activity, which can be achieved through careful selection of PEG size, attachment site, and chemistry .

What analytical techniques are most effective for characterizing PRLR-ligand interactions?

Multiple analytical techniques are effective for characterizing PRLR-ligand interactions, each offering unique insights. Surface plasmon resonance (SPR) provides real-time binding kinetics and affinity constants between PRLR-ECD and various ligands . Size-exclusion chromatography under non-denaturing conditions can assess the formation of stable complexes and determine their stoichiometry . Competitive binding assays using biotinylated ligands can evaluate the relative affinities of different compounds . For structural insights, X-ray crystallography and cryo-electron microscopy can reveal the three-dimensional organization of receptor-ligand complexes. Hydrogen-deuterium exchange mass spectrometry can identify regions involved in binding by measuring changes in solvent accessibility. These complementary approaches provide comprehensive characterization of PRLR-ligand interactions for both basic research and drug development purposes .