What are the auditor's responsibilities to communicate information to the audit committee under AICPA and PCAOB standards?

Question:

What are the auditor's responsibilities to communicate information to the audit committee under AICPA and PCAOB standards? If the auditor discovers that the audit committee routinely ignores such communications, especially when they are critical of management's use of in the financial statements, what step(s) might the auditor take at this point?
GAAP
Generally Accepted Accounting Principles (GAAP) is the accounting standard adopted by the U.S. Securities and Exchange Commission (SEC). While the SEC previously stated that it intends to move from U.S. GAAP to the International Financial Reporting Standards (IFRS), the...