Question

I'm just looking for a better understanding of the process of what happens in each part that follows. What information should I include to help with understanding the question? In Part A, I'm asking about how a neutrophil chasing a bacterium detects and moves towards the bacterium. Then, how does the neutrophil change its course. Processes that I need help understanding and would like included in the explanation if possible are listed after the question. Part B asks how a constant activation of Ras causes increased expression of Cyclin D and S Phase genes by transcription factor E2F. The terms that follow would be helpful in the explanation. I'm not sure how else to phrase part C.

1. Discuss how a neutrophil that is after a bacterium will detect and move toward the bacterium and how the neutrophil will change course when needed.

Include in explanation the role or function of the following:

1. • Chemical gradient,  N-formyl peptide receptor,  G_βγ (βγ subunit of the G protein-coupled receptor),  RacGEF, RacGDP, RacGTP,  WASP, Arp2/3,  Actin nucleation, 70° branching,  Lamellopodium,  CapZ, and Myosin
2. If the GTPase function of Ras is destroyed it will always be bound to GTP in an initiating event in cancers.  Explain how the always on activation of Ras causes increased expression Cyclin D and S Phase genes by transcription factor E2F.  

Include in explanation the role or function of the following and whether the protein is a kinase or transcription factor:

• Raf, MEK, ERK
• Myc
• Cyclin D/Cdk4 or Cdk 6
• Rb
• E2F

3. What is the effect and purpose of the two positive feedback loops that occur in E2F activation.  (When E2F is activated, it can amplify its own gene expression and cause transcription of Cyclin E.  Cyclin E with Cdk2 can phosphorylate Rb, removing Rb’s inhibitory effect on E2F).

Answer 1

A.

Chemical gradient:

The dynamics of neutrophil chemotaxis was studied under competing for chemoattractants like leukotriene B4, chemokine C–X–C motif ligands 2 and 8, and fMLP. There was a specific level of a hierarchy of these chemoattractants like fMLP > CXCL8 > CXCL2 > leukotriene In most of the conditions, over 60% of neutrophils exposed to a gradient move toward the robust signal though the weaker chemoattractant influences neutrophil motility.

N-formyl peptide receptor: G-protein–coupled formyl peptide receptors (FPRs) directly interfere with neutrophil phagocytosis. In mouse neutrophils without formyl peptide receptors (Fpr1/2–/–) are defective in the process of phagocytosis of Escherichia coli.FPRs areG-protein-coupled receptors (GPCRs) present on neutrophils that function as chemoattractant receptors in innate immune responses.

Gβγ (βγ subunit of the G protein-coupled receptor):

After binding of formyl peptides to FPRs encourages dissociation of heterotrimeric G proteins into Gαi and Gβγ, which further activate downstream signal transduction pathways, regulates the spatiotemporal organization of the actin cytoskeleton and helps in cell migration.

RacGEF, RacGDP, RacGTP:

Rac proteins are tiny Rho family guanine‐nucleotide binding proteins (G proteins, GTPases). These GTPases control the structure of the actomyosin cytoskeleton mainly through IRSp53, WAVE and Arp2/3, thus helps the polymerization of branched actin filaments at the neutrophil periphery. Rac signalling pathways that control actomyosin cytoskeletal dynamics are essential for neutrophil adhesion, spreading and the formation of a leading-edge that converses cell polarization and migration. , Rac‐GTPases also control other responses which require cytoskeletal dynamics, such as the degranulation of azurophil granules and integrin‐dependent phagocytosis. Active Rac2 is a crucial component of the NADPH oxidase (NOX2) enzyme complex so it directly involved in ROS production. In turn, ROS is required to make NETs, and both are crucial responses for killing pathogens.

WASP:

Rho GTPase Cdc42 controls neutrophil polarity through CD11b signalling. Here, we show that Cdc42 controls polarity by WASp. Cdc42 controls WASp activation and its distant localization to the uropod. WASp mediates long-distance control of the uropod by Cdc42 to maintain a proper balance between the pseudopod and the uropod.

Arp2/3:

Rac-GTPs activates downstream signalling of IRsp53 which further activates its downstream partner WAVE that inturns activate Arp2/3 which helps in the polymerization of branched-chain actin filaments at the leading edge.

Actin nucleation, 70° branching,  Lamellopodium:

Actin The Arp2/3 complex is present in lamellipodia and pseudopodia. It plays a role in membrane protrusion. It nucleates actin filaments that elongate at their barbed ends of the cell. The nucleation activity of the complex is accompanied by its ability to occupy, or cap, the pointed ends of actin filaments. Thus, a single molecule of the Arp2/3 complex can bind simultaneously to the pointed end of one actin filament and to the side of another actin filament, thereby crosslinking the filaments into branched formations. Active Arp2/3 complex along with WASP helps in 70° branching.