a. Two arrestin genes (β -arrestin 1 and 2) have been characterized and are expressed ubiquitously. Over the past several years, the development of knockout mice in which the genes for β-arrestin 1 and 2 have been inactivated have greatly aided the study of the physiological and cellular roles of these multifunctional proteins.
To better understand the role of β-arrestin 1 and 2 in the desentitization of the β2 - R small interfering RNA (RNAi) were used to specifically suppress the expression of β arrestin 1 or 2 or both. The results are shown in the figure below.
What does this figure show in term of specificity of the two siRNA molecules (β-arr1 and β -arr2)?
b. The effect of the siRNA -mediated β-arrestin depletion on cAMP accumulation by endogenously expressed β-AR2. The cells were transfected with the indicated siRNA molecules and subsequently stimulated with isoproterenol (epinephrine).
As a control the cells were not stimulated with Isoproterenol (NS). Data are expressed as percent of agonist-induced cAMP accumulation in control RNA-treated cells. What β arrestin protein (1 or 2) participates in the desensitization of the β -AR2? Justify your answer.