cell communication

1. cell communication

2. course layout • introduction • molecular biology • biotechnology • bioMEMS • bioinformatics • bio-modeling • cells and e-cells • transcription and regulation • cell communication • neural networks • dna computing • fractals and patterns • the birds and the bees ….. and ants

3. introduction

4. cell communication

5. what is signal transduction? • Conversion of a signal from one physical or chemical form into another. • In cell biology, it commonly refers to the sequential process initiated by binding of an extracellular signal to a receptor and culminating in one or more specific cellular responses.

6. what is a signal transduction pathway? • Chemical signals are converted from one type of signal into another to elicit a molecular response from the organism. All organisms require signaling pathways to live. • Letters represent chemicals or proteins. Arrows represent enzymatic steps. ABCDEFG

7. what is a second messenger? • An intracellular signaling molecule whose concentration increases (or decreases) in response to binding of an extracellular ligand to a cell-surface receptor.

8. cell signaling • How do cells receive and respond to signals from their surroundings? • Prokaryotes and unicellular eukaryotes are largely independent and autonomous. • In multi-cellular organisms there is a variety of signaling molecules that are secreted or expressed on the cell surface of one cell and bind to receptors expressed by other cells. These molecules integrate and coordinate the functions of the cells that make up the organism.

9. modes of cell-cell signaling Direct • cell-cell or cell-matrix Secreted molecules. • Endocrine signaling. The signaling molecules are hormones secreted by endocrine cells and carried through the circulation system to act on target cells at distant body sites. • Paracrine signaling. The signaling molecules released by one cell act on neighboring target cells (neurotransmitters). • Autocrine signaling. Cells respond to signaling molecules that they themselves produce (response of the immune system to foreign antigens and cancer cells).

10. steroid hormones • This class of molecules diffuse across the plasma membrane and binds to Receptors in the cytoplasm or nucleus. The y are all synthesized from cholesterol. • They include sex steroids (estrogen, progesterone, testosterone) corticosteroids (glucocorticoids and mineralcorticoids) Thyroid hormone, vitamin D3, and retinoic acid have different structure and function but share the same mechanism of action with the other steroids. • Steroid Receptor Superfamily. They are transcription factors that function either as activators or repressors of transcription.

11. steroid hormones

12. seven levels of regulation of cell growth

13. pathways are inter-linked Signalling pathway Genetic network STIMULUS Metabolic pathway

14. metabolic pathways 1993 Boehringer Mannheim GmbH - Biochemica

15. overview of cell to cell communication Chemical • Autocrine & Paracrine: local signaling • Endocrine system: distant, diffuse target Electrical • Gap junction: local • Nervous system: fast, specific, distant target

16. gap junctions and CAMs • Protein channels - connexin • Direct flow to neighbor • Electrical- ions (charge) • Signal chemicals • CAMs (cell-adhesion molecules) • Need direct surface contact • Signal chemical Figure 6-1a, b: Direct and local cell-to-cell communication

17. gap junctions and CAMs Figure 6-1a, b: Direct and local cell-to-cell communication

18. paracrines and autocrines • Local communication • Signal chemicals diffuse to target • Example: Cytokines • Autocrine–receptor on same cell • Paracrine–neighboring cells Figure 6-1c: Direct and local cell-to-cell communication

19. hormones • Signal Chemicals • Made in endocrine cells • Transported via blood • Receptors on target cells long distance communication Figure 6-2a: Long distance cell-to-cell communication

20. neurons and neurohormones Neurons • Electrical signal down axon • Signal molecule (neurotransmitter) to target cell Neurohormones • Chemical and electrical signals down axon • Hormone transported via blood to target long distance communication Figure 6-2 b: Long distance cell-to-cell communication

21. neurons and neurohormones long distance communication Figure 6-2b, c: Long distance cell-to-cell communication

22. neurons and neurohormones long distance communication Figure 6-2b, c: Long distance cell-to-cell communication

23. signal pathways • Signal molecule (ligand) • Receptor • Intracellular signal • Target protein • Response Figure 6-3: Signal pathways

24. receptor locations Cytosolic or Nuclear • Lipophilic ligand enters cell • Often activates gene • Slower response Cell membrane • Lipophobic ligand can't enter cell • Outer surface receptor • Fast response

25. membrane receptor classes • Ligand- gated channel • Receptor enzymes • G-protein-coupled • Integrin

26. membrane receptor classes

27. signal transduction • Transforms signal energy • Protein kinase • Second messenger • Activate proteins • Phosporylation • Bind calcium • Cell response

28. signal amplification • Small signal produces large cell response • Amplification enzyme • Cascade

29. receptor enzymes • Transduction • Activation cytoplasmic • Side enzyme • Example: Tyrosine kinase Figure 6-10: Tyrosine kinase, an example of a receptor-enzyme

30. G-protein-coupled receptors • Hundreds of types • Main signal transducers • Activate enzymes • Open ion channels • Amplify: • adenyl cyclase-cAMP • Activates synthesis

31. G-protein-coupled receptors

32. transduction reviewed

33. novel signal molecules • Calcium: muscle contraction • Channel opening • Enzyme activation • Vesicle excytosisNitric Oxide (NO) • Paracrine: arterioles • Activates cAMP • Brain neurotransmitter • Carbon monoxide (CO)

34. novel signal molecules Calcium as an intracellular messenger

35. quorum sensing

36. quorum sensing • the ability of bacteria to sense and respond to environmental stimuli such as pH, temperature, the presence of nutrients, etc has been long recognized as essential for their continued survival • it is now apparent that many bacteria can also sense and respond to signals expressed by other bacteria • quorum sensing is the regulation of gene expression in response to cell density and is used by Gram positive and Gram negative bacteria to regulate a variety of physiological functions • it involves the production and detection of extracellular signaling molecules called autoinducers

37. quorum sensing • Tomasz (1965) – Gram-positive Streptococcus pneumoniae produce a “competence factor” that controlled factors for uptake of DNA (natural transformation) • Nealson et al. (1970) – luminescence in the marine Gram-negative bacterium Vibrio fischeri controlled by self-produced chemical signal termed autoinducer • Eberhard et al. (1981) identified the V. fischeri autoinducer signal to be N-3-oxo-hexanoyl-L-homoserine lactone • Engebrecht et al. (1983) cloned the genes for the signal generating enzyme, the signal receptor and the lux genes

38. quorum sensing • Vibrio fischeri is a specific bacterial symbiont with the squid Euprymna scolopes and grows in its light organ

39. quorum sensing • the squid cultivates a high density of cells in its light organ, thus allowing the autoinducer to accumulate to a threshold concentration • at this point, autoinducer combines with the gene product luxR to stimulate the expression of the genes for luciferase, triggering maximal light production • studies have shown that hatchling squid fail to enlarge the pouches that become the fully developed organ when raised in sterile seawater

40. quorum sensing In V. fisheri, bioluminsecence only occurs when V. fischeri is at high cell density

41. quorum sensing N-3-oxo-hexanoyl-L-homoserine lactone

42. quorum sensing • Fuqua et al. (1994) introduced the term quorum sensing to describe cell-cell signaling in bacteria • Early 1990’s – homologs of LuxI were discovered in different bacterial species • V. fischeri LuxI-LuxR signaling system becomes the paradigm for bacterial cell-cell communication

43. quorum sensing • Vast array of molecules are used as chemical signals – enabling bacteria to talk to each other, and in many cases, to be multilingual Gram-negative bacteria Gram-positive bacteria universal language

44. quorum sensing in Pseudomonas aeruginosa • P. aeruginosa uses a hierarchical quorum sensing circuit to regulate expression of virulence factors and biofilm formation

45. quorum sensing in Gram-positive bacteria • Gram-positive bacteria utilizes modified oligopeptides as signaling molecules – secreted via an ATP-binding cassette (ABC) transporter complex • Detectors for these signals are two-component signal transduction systems

46. quorum sensing in Gram-positive bacteria sensor kinase binding of autoinducer leads to autophosphorylation at conserved histidine residue response regulator -phosphorylation at conserved aspartate by sensor kinase leads to binding of regulator to specific target promoters

47. hybrid quorum sensing circuit in Vibrio harveyi • V. harveyi –marine bacterium, but unlike V. fischeri, does not live in symbiotic associations with higher organisms, but is free-living • Similar to V. fischeri, V. harveyi uses quorum sensing to control bioluminescence • Unlike V. fischeri and other gram-negative bacteria, V. harveyi has evolved a quorum sensing circuit that has characteristics typical of both Gram-negative and Gram-positive systems

48. hybrid quorum sensing circuit in Vibrio harveyi • V. harveyi uses acyl-HSL similar to other Gram-negatives but signal detection and relay apparatus consists of two-component proteins similar to Gram-positives • V. harveyi also responds to AI-2 that is designed for interspecies communication X = transcriptional repressor

49. hybrid quorum sensing circuit in Vibrio harveyi AI-1 AI-2 LuxN and LuxQ – autophosphorylating kinases at low cell densities Accumulation of autoinducers – LuxN and LuxQ  phosphatases draining phosphate from LuxO via LuxU Dephosphorylated LuxO is inactive  repressor X not transcribed X = transcriptional repressor

50. LuxS and interspecies communication • LuxS homologs found in both Gram-negative and Gram-positive bacteria; AI-2 production detected in bacteria such as E. coli, Salmonella typhimurium, H. pylori, V. cholerae, S.aureus, B. subtilis using engineered V. harveyi biosensor • Biosynthetic pathway, chemical intermediates in AI-2 production, and possibly AI-2 itself, are identical in all AI-2 producing bacteria to date – reinforces the proposal of AI-2 as a “universal” language